Fetal NT-proBNP levels and their course in severe anemia during intrauterine treatment

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We examined the effect of anemia and intrauterine transfusion (IUT) on NT-proBNP concentrations in fetuses with anemia and established gestational age-dependent reference values of a control group. Methods We analyzed NT-proBNP levels in anemic fetuses that underwent serial intrauterine transfusions (IUT), focusing on different causes and severity of anemia and comparing the results to a non-anemic control group. Results In the control group, the average NT-proBNP concentration was 1339 ± 639 pg/ml, decreasing significantly with increasing gestational age (R=-74.04, T=-3.65, p=0.001). Subjects had significantly higher NT-proBNP concentrations before initiation of IUT therapy (p<0.001), showing fetuses with parvovirus B19 (PVB19) infection having the highest concentrations. Hydropic fetuses also showed an increased in NT-proBNP concentration compared to non-hydropic fetuses (p<0.001). During the course of therapy, NT-proBNP concentration before subsequent IUT decreased significantly from pathologically high levels, while MoM-Hb and MoM-MCA-PSV remained pathological. Conclusion NT-pro BNP levels in healthy fetuses are higher than in postnatal life, decreasing with ongoing pregnancy. Anemia is a hyperdynamic state and its severity correlates with circulating NT-proBNP levels. Highest concentrations occur in fetuses with hydrops and with PVB19 infection, respectively. Treatment by IUT leads to a normalisation of NT-proBNP concentrations, so the measurement of its levels may be useful in therapy monitoring. fetal anemia hydrops fetalis Parvovirus B19 infection Rhesus incompatibility intrauterine transfusion Figures Figure 1 Figure 2 Figure 3 Introduction Severe anemia of the fetus is defined as low cord blood concentration of haemoglobin (Hb) more than 7–10 g/dl below the mean for gestational age [ 1 ]. Causes can be immunological (alloimmunization), such as Rhesus incompatibility, or non-immunological, such as PVB19 infections. Ultrasound findings signalling hydrops fetalis (skin edema, ascites, hydrothorax, cardiomegaly, placentomegaly, polyhydramnios) and an increased peak systolic velocity of the middle cerebral artery (MCA-PSV), measured by Doppler ultrasound, lead to the diagnosis [ 2 ]. Fetal anemia causes increased cardiac output and hyperdynamic circulatory adaptions, such as increased myocardial stretching, wall stress and filling pressures that cause cardiac remodelling and cardiomegaly. In fetuses with severe anemia, a marked increase in coronary perfusion can be demonstrated by Doppler echocardiography [ 3 ]. Coronary perfusion of the hypertrophic myocardium may increase up to fivefold, but when those adapting mechanisms are exhausted, myocardial ischemia occurs. Severe fetal anemia can cause heart failure with hydrops, as the fetal compartiments react sensitively to circulatory stress and intrauterine demise becomes imminent [ 4 ]. N-terminal pro-B-type (NT-proBNP) is a marker of cardiac dysfunction and myocardial remodelling, known in adult [ 5 ], as well as fetal medicine [ 6 ]. Its circulating levels correlate with myocardial wall stress, cardiac workload and an increased central venous pressure [ 7 ]. In the fetus, the natriuretic system, which regulates blood-pressure by diuresis and vasodilatation, starts at mid-gestation [ 8 ]. Various studies presented normal values for newborns and children [ 9 ] but only very few report on the circulating concentration prenatally [ 10 ]. Increased NT-proBNP levels have been presented in fetuses with cardiovascular dysfunctions, such as structural cardiac malformations [ 11 ], as well as in fetuses with anemia [ 12 ], but also in fetuses with urinary tract malformations [ 13 ] or severe growth restriction [ 14 ]. Few studies have presented NT-proBNP values during treatment with intrauterine transfusions [ 12 , 15 ]. Having doubled our numbers over the past decade, in this study, we aimed to update information on fetal NT-proBNP values, stating normal values during pregnancies of fetuses without increased cardiac load, and comparing those to anemic fetuses during treatment with serial intrauterine transfusions. Methods This retrospective study included all fetuses receiving intrauterine transfusion (IUT) (subjects) between March 2009 and October 2020 and fetuses that underwent feticide by intravascular injection of potassium chloride, without a suspected disease that could influence fetal NT-proBNP levels (controls) between January 2017 and October 2020 at the tertiary center for Prenatal Medicine of the University of Bonn. In our center we perform about 50 IUTs and 100 feticides annually. Ethical approval was achieved by the Ethics Committee of the University of Bonn. All fetuses underwent a detailed scan, using high-resolution ultrasound equipment, before each puncture (each IUT and feticide), including Doppler sonographic measurements of the arteria umbilicalis, ductus venosus and MCA. To assess fetal anemia the MCA-PSV was measured, with an insonation angle of < 10° and calculated in multiples of the median (MoM) by the formula e (2.31+0.046/GA) . Hb values were determined before transfusion or feticide and were converted to MoM-Hb values. A MoM-Hb value of 0.84 − 0.65 indicated mild anemia, MoM-Hb values of 0.64 − 0.55 moderate anemia, and MoM-Hb values of 1:32 for Rhesus-antibodies (CcDEe), Rhesus incompatibility was diagnosed. PVB19 infection was confirmed either by PCR of fetal blood/amniotic fluid or by maternal IgM antibodies and sonographic signs for severe anemia. Hydrops fetalis was diagnosed when at least two of the following signs were present, including at least one fetal compartiment: ascites, hydrothorax, pericardial effusion, skin edema, and placentomegaly, cardiomegaly or polyhydramnios. Intrauterine growth restriction (IUGR) was defined as an estimated fetal weight percentile < 10%. The following parameters were analyzed from the fetal blood samples: NT-proBNP (pg/ml) and haemoglobin (g/dl). We assessed the gestational age at first presentation at our center, at the puncture (each IUT and feticide) and outcome measures. All fetuses that underwent serial IUTs due to anemia belonged to this group. We excluded anemic fetuses with growth restriction before the first IUT. 10 fetuses in this group have been described in a previous publication [ 12 ]. For the puncture we used a 22G-needle, which was guided into the umbilical vein by ultrasound. Subjects: Fetal blood sampling was initiated, followed by the IUT. To avoid volume overload, we applied no more than 30-50ml per kilogram estimated fetal weight (without hydrops), using cross-matched, 0 Rhesus-negative and cytomegaly virus-negative, irradiated packed red blood cells. In cases of severe anemia we performed a subsequent IUT 2–5 days later if the haemoglobin concentration was below 10g/dl at the end of IUT. Follow-up ultrasound and Doppler scans were achieved on the next day, followed by weekly scans. We collected the number of performed IUTs and the interval between IUTs. Controls: Feticide was performed according to the national legislation, and all fetuses offering conditions that may influence the blood levels of NT-proBNP were excluded, such as cardiovascular dysfunctions (cardiac or thoracic malformations, infections, hydrops), urinary tract malformations, tumors, neuromuscular disorders, growth restriction, pathological Doppler assessment (high resistance in the umbilical artery or ductus venosus) and monochorionic multiple pregnancies. For feticide, the umbilical vein was punctured by a 22G-needle under ultrasound control and before injection of the potassium chloride, fetal blood was withdrawn for analysis. Fetuses with proven anemia in the blood sample or with suspected anemia, showing increased MCA-PSV were excluded from the control group. All examined values were tested for normal distribution using the Kolmogorov-Smirnov test. Parameters showing positive skewness, such as NT-proBNP concentration, were considered logarithmized. The following influences on blood analysis variables in the control group were examined using multiple linear regressions: Child sex and disease, maternal BMI and age and gestational age. All requirements for a multiple linear regression were met; residuals were tested for normal distribution using the Shapiro-Wilk test. For comparison of means between subgroups, analysis of variance (ANOVA) and the Bonnferoni post-hoc test as well as the Games-Howell post-hoc test were performed. Linear correlations within groups were estimated with the Pearson correlation coefficient. The course of blood test results of sequential IUTs was explored using a linear mixed model. The significance level was set at p < 0.05 for each analysis. We used IBM SPSS Statistics 27.0 for data analyses. We analyzed the normal blood values of NT-proBNP in fetuses that underwent feticide and not showing any signs or diseases that could affect the natriuretic system and compared our results to the norm values of Merz et al [ 16 ]. Comparing controls and subjects, we analyzed the effect of anemia and the IUT-therapy on the NT-proBNP-level. Within the anemic group we performed two subanalyses. First, we analyzed if there were differences in the circulating NT-proBNP levels, comparing cases with Rhesus incompatibility with those affected by a PVB19 infection and the influence of the diagnosis of fetuses with hydrops. Second, we analyzed the course of the NT-proBNP levels during serial IUT therapy. Results 86 fetuses, whose blood samples were taken during feticide, presented the control group. 190 feticides had to be excluded, as the fetuses presented with diagnoses that might have had an impact on NT-proBNP levels. Reasons for feticide are listed in Table 1 . The subject group consisted of 183 fetuses, which received IUT. We excluded 63 monochorionic twin pregnancies, 3 triplets and 10 IUGRs, leaving n = 107 for analysis. Reasons for fetal anemia are listed in Table 1 . 54 subjects showed hydrops fetalis and were investigated as a subgroup. 41 fetuses had Rhesus incompatibility and 29 a PVB19 infection. Table 1 Diagnosed diseases in the group of controls and subjects Data in number n (%) Disease Controls Subjects Number of hydropic fetuses Skeletal dysplasia 5 (5.8) Rhesus incompatibility 41 (38.3) 15/41 (36.6) Neural tube defects 15 (17.4) Parvovirus B19 29 (27.1) 18/29 (62.1) Brain Malformations 39 (45.3) Kell anemia 8 (7.5) 4/8 (50.0) Trisomy 21 14 (16.3) Cytomegaly virus 3 (2.8) 3/3 (100.0) Chromosomal aberrations 2 (2.3) Chorangioma 3 (2.8) 1/3 (33.3) Diverse 11 (12.8) Homozygotic alpha-Thalassemia 1 (0.9) 1 (100.0) Congenital dyserythropoetic anemia 1 (0.9) 0 Trisomy 21 1 (0.9) 1 (100.0) Anemia for other or unknown etiology 20 (18.7) 11 (55.0) Total 86 (100) 107 (100) 54/107 (50.0) The median interval between the first and the second IUT was 7 days (n = 107, SD = 0.70), and 13 days between the second and the third IUT (n = 84, SD = 1.05). Of the 107 fetuses that underwent serial IUT, 91 were born alive at a median gestational age of 35.1weeks (SD = 3.7) and a birth weight of 2692 ± 724 on a centile of 49 ± 27. Eleven subjects suffered intrauterine fetal death (IUD). Seven of these fetuses had a PVB19 infection with severe hydrops fetalis. Of those eleven IUDs, five occurred within 24 hours after the transfusion. Five children died postnatally. In all of these neonatal deaths (NND), hydrops fetalis was diagnosed during pregnancy. Two of them were delivered at 27 weeks with severe anemia of unknown cause, one at 28 weeks with CMV infection, one at 32 weeks with trisomy 21 and one at 21 weeks with multiple chroangiomata. In five cases, no information on the outcome could be collected. Baseline characteristics, Doppler measurements and blood parameters of subjects and controls, as well as the subgroups Rhesus incompatibility and PVB19 are listed in Table 2 . Maternal age and body mass index (BMI) as well as the distribution of the fetal sex were comparable in the groups. Table 2 Basic characteristics and measurements of the patient collective Subjects n = 107 Subgroup Rhesus Incompatibility n = 41 Subgroup PVB19 n = 29 Controls n = 86 Maternal characteristics Age mother [years] a 31.4 ± 5.3 32.0 ± 1.5 31.2 ± 5.5 31.4 ± 5.3 BMI mother [kg/m²] a 26.1 ± 4.5 27.1 ± 4.9 26.2 ± 4.4 27.8 ± 5.7 Gravidity of the mother a 3.0 ± 1.6 4.2 ± 1.5 2.7 ± 1.3 2.4 ± 1.3 Mother parity a 1.0 ± 1.3 2.0 ± 1.5 1.1 ± 0.9 1.0 ± 1.0 GA at first intervention [week, days] a 23.6 ± 6.5 25.3 ± 5.0 19.5 ± 2.6 25.0 ± 3.7 Fetal characteristics Male fetuses b 51 (47.7) 22 (53.7) 15 (51.7) 38 (44.2) Female fetuses b 53 (49.5) 17 (41.5) 14 (48.3) 48 (55.8) Dichorionic twins b 5 (4.7) 2 (4.9) 1 (3.4) 5 (5.8) Estimated weight [g] a 843 ± 627 1081 ± 664 356 ± 145 704 ± 442 Hydrops fetalis b 54 (50.5) 15 (36.6) 18 (62.1) 0 Outcome Live births b 91 (80.4) 37 (90.2) 22 (75.9) 0 Birth weight (BW) [g] a 2692 ± 724 2658 ± 584 2950 ± 1078 Percentile of BW b 49 ± 27 53 ± 27 36 ± 25 Intrauterine death (IUD) a 11(10.3) 0 7 (24.1) No information b 5 (4.7) 4 (9.7) 0 a Data in mean (M) ± standard deviation (SD) b Data in number n (%) The NT-proBNP concentration in the control group showed a mean of 1339 ± 639 pg/ml. There was a significant decline in NT-proBNP concentration with advancing gestational age (p = 0.001), showing an average decrease of 74 pg/ml per week of gestation. Overall, the mean dropped from 1813 pg/ml at 19 weeks to 702 pg/ml at week 34 (see Fig. 1). There was one outlier in the group with a NT-proBNP value of 4413 pg/ml. This fetus had a normal Hb and was not anemic. Feticide was performed for open spina bifida. The different fetal diagnoses, maternal age and BMI showed no influence on NT-proBNP concentration in the multiple linear regression (p > 0.05). Only male sex showed a slightly increased NT-proBNP concentration compared to the female sex (p = 0.006, β = 0,34, R = 431). However, the strength of this influence was lower, measured by standardized coefficient ((β) = 0.3), than the influence of gestational age (β = 0.5). In the group of subjects, there was a strong correlation between the severity of fetal anemia (MoM-Hb) and both, NT-proBNP values (R=-0.64, p < 0.001) as well as MoM-MCA-PSV values (R=-0.50, p < 0.001). ANOVA showed significant differences in the NT-proBNP levels (F = 48.5, p < 0.001), MoM-Hb values (F = 81.62, p < 0.001) and MoM-MCA-PSV values (F = 68.81 p < 0.001), comparing controls and subjects, subgroups of fetuses with PVB19 infection and fetuses with Rhesus incompatibility as well as fetuses with and without hydrops fetalis in the fetal blood before the start of therapy, compared to the controls at the time of feticide (see Fig. 2). The subgroup of anemic fetuses with PVB19 infection showed the highest blood levels of NT-proBNP concentration, compared to the control group (p < 0.001) and compared to the subgroup of Rhesus incompatibility (p = 0.026) (see Fig. 2). But the mean value of fetuses with Rhesus incompatibility was also significantly higher compared to the control group (p < 0.001). MoM-MCA (p = 0.330) and MoM-Hb levels (p = 0.892) did not show a significant difference between fetuses of Rhesus incompatibility and fetuses with PVB19 infection. Moreover, fetuses with hydrops showed significantly higher NT-proBNP levels compared to anemic fetuses without hydrops (p = 0.006), and also compared to controls (p < 0.001). Before the start of therapy, subjects with hydrops fetalis showed a mean NT-proBNP concentration of 21959 ± 219959 pg/ml, whereas fetuses without hydrops showed a mean of 52946 ± 54777 pg/ml. Those observations could also be made for MoM-Hb (p < 0.001) and MoM-MCA (p = 0.049) when comparing the hydropic fetuses to non-hydropic fetuses. During therapy, NT-proBNP (β=-0.14, p < 0.001, 95%CI=-0.17 to -0.11) and MoM-MCA-PSV (β=-0.09, p < 0.001, 95%CI=-1.1 to -0.07)) values significantly decreased, while the MoM-Hb (β = 0.05, p < 0.001, 95%CI = 0.04 to 0.06) values significantly increased (see Fig. 3 and Table 3 ). The greatest change in all parameters occurred between the first and second transfusion. The median of NT-proBNP decreased 47% between the first and second IUT (95%CI=-63% to -31%) and 36% between the second and third IUT (95%CI=-62% to -10%). Based on the GA-dependent values obtained, only 5% of the measured NT-proBNP concentrations were within the physiological range before the first IUT. After the third IUT, it was 63% of the measured values (n = 14). Thus, more fetuses had physiological NT-proBNP concentrations than pathological NT-proBNP concentrations. MoM-Hb values increased from a median of 0.42 (Q1-Q3 = 0.24–0.58) to a median of 0.78 (Q1-Q3 = 0.55–0.84) from first to second IUT. MoM-MCA-PSV values decreased from a median of 2.12 (Q1-Q3 = 1.78–2.36) to 1.59 (Q1-Q3 = 1.33–1.95) from first to second IUT. Overall, levels of MoM-MCA-PSV and MoM-Hb remained pathological before each transfusion. See Table 3 for the measured values before each IUT. Table 3 Measurements of different parameters in controls subjects and subgroups before feticide (FC) (controls) or each intrauterine transfusion (IUT) (subjects). NT-proBNP [pg/ml] MoM-MCA-PSV MoM-Hb FC Controls n = 86 1399 ± 639 [58] 1.00 ± 0.21 [63] 1.04 ± 0.10 [54] IUT 1 Subjects n = 107 37452 ± 44205 [54] 2.12 ± 0.42 [107] 0.43 ± 0.21 [100] Rhesus Incompatibility n = 41 27937 ± 37680 [ 23 ] 2.05 ± 0.42 [ 41 ] 0.44 ± 0.21 [ 40 ] PVB19 n = 29 46420 ± 36982 [ 14 ] 2.22 ± 0.39 [ 29 ] 0.40 ± 0.20 [ 24 ] IUT 2 Subjects n = 80 28490 ± 57721[ 39 ] 1.65 ± 0.41 [80] 0.66 ± 0.18 [79] Rhesus Incompatibility n = 36 9366 ± 14261 [ 16 ] 1.59 ± 0.36 [ 36 ] 0.68 ± 0.21 [ 37 ] PVB19 n = 15 33677 ± 20504 [ 8 ] 1.71 ± 0.39 [ 15 ] 0.63 ± 0.18 [ 14 ] IUT 3 Subjects n = 56 6453 ± 7793 [ 28 ] 1.60 ± 0.35 [56] 0.66 ± 0.20 [52] Rhesus Incompatibility n = 35 5078 ± 6336 [ 16 ] 1.59 ± 0.40 [ 35 ] 0.67 ± 0.20 [ 32 ] PVB19 n = 4 22603 ± 16249 [ 2 ] 1.69 ± 0.36 [ 4 ] 0.71 ± 0.12 [ 4 ] IUT 4 Subjects n = 44 6710 ± 11933 [ 22 ] 1.59 ± 0.44 [44] 0.70 ± 0.19 [43] Rhesus Incompatibility n = 28 7882 ± 14152 [ 13 ] 1.60 ± 0.50 [ 28 ] 0.69 ± 0.21 [ 28 ] Values in mean ± SD [measured values] Author Contribution All authors contributed to the study conception and design. Material, preparation, data collection and analysis were performed by P. Siebers and E. Weber, who have written the first draft of the manuscript. All authors commented on previous versions, read and approved the final manuscript. P Siebers: Data Collection, Manuscript writing U Gembruch: Project development, Manuscript editing WM Merz: Project development, Manuscript editing F Recker: Data Collection, Manuscript editing A Müller: Manuscript editing B Strizek: Manuscript editing C Berg: Manuscript editing EC Weber: Data Collection, Project development, Manuscript writing Throughout the course of IUT therapy, the differences in parameters described at the beginning remained (see Fig. 3). Hydropic fetuses showed higher levels of NT-proBNP in the cord-blood than non-hydropic fetuses (β = 0.34, p = 0.001, 95%CI = 0.54 to 0.15). MoM-Hb-values were significantly lower during IUT-therapy in hydropic fetuses (ß=-0.11, p < 0.001, 95%CI = 0.06 to 0.17). Only MoM-MCA-PSV did not show significant differences during therapy (p = 0.279). Fetuses with PVB19 infection showed significantly higher NT-proBNP levels compared to fetuses with Rhesus incompatibility during the first three IUTs (ß=0.58, p < 0.001, 95%CI = 0.88 to 0.27). Discussion Because of its long half-life and high thermostability, NT-proBNP is an established marker for cardiac function in adults. In contrast to image-based diagnostics, there is no inter- or intraobserver variability. The correlation between cardiac stress and NT-proBNP concentration also appears to be strong in the fetal organism [ 7 , 11 , 17 , 18 ]. Although MCA-PSV measurement shows high reliability for anemia diagnosis, it cannot reliably predict the occurrence of hydrops fetalis [ 19 ] and the severity of cardiac compromise and is affected during IUT therapy by transfused adult erythrocytes [ 20 ]. Physiological reference values of NT-proBNP concentration in fetal blood are difficult to define due to ethical considerations of the invasive procedure and different analytical methods [ 21 ]. So far, there are only very few studies that deal with this topic. Fortunato et al. [ 22 ] performed blood sampling in a cohort of 22 fetuses in the second trimester. The mean NT-proBNP concentration was 2308 pg/ml. Exclusion criteria were multiple pregnancies, severe fetal anomalies, and abnormal karyotypes. Walther et al. [ 23 ] calculated an average NT-proBNP concentration of 1052 ± 182 pg/ml in the fetal blood of 9 fetuses. Blood samples were taken on the suspicion of fetal infection in the second trimester, which was not confirmed in the blood analysis. Both studies had a small number of cases and were limited to values before the 25 week of gestation. Merz et al. [ 10 ] determined a mean NT-proBNP concentration in 59 fetuses of 1998 pg/ml (± 2SD = 242–3754) between 20 and 34 weeks of gestation. Exclusion criteria included structural malformations of the cardiovascular and urogenital systems and conditions with potential influence on NT-proBNP concentration. In our study, the average measured NT-proBNP concentration was 1339 ± 639 pg/ml between 20 and 35 weeks' gestation (n = 58), so it correlates with the previous data, using the same analytical procedure. Besides Merz et al. our results represent the largest sample size for normal NT-proBNP values in accordance to gestational age up to 35 weeks of gestation. Our regression analysis showed a significant decrease in NT-proBNP concentration with increasing gestational age (-74.04*GA + 3220 pg/ml, p = 0.001), which correlates well to the regression calculated by Merz et al. (-74.8*GA + 3946 pg/ml, p = 0.012) (see Fig. 1). NT-proBNP concentrations in umbilical cord samples in term pregnancies are significantly lower than values measured in the second trimester [ 22 , 24 ]. Compared to adult reference values (0–10 pg/ml) and NT-proBNP blood concentration of pregnant women, fetal blood levels are significantly higher. Placental exchange during pregnancy and lack of renal elimination were excluded as causes [ 8 , 22 , 25 ]. The higher NT-proBNP concentration appears to result from intrinsic fetal production of this hormone [ 16 ]. Natriuretic peptides are involved in the development of various organ systems during the fetal period and are mainly responsible for the growth of cardiovascular tissue. Animal experiments have shown that both, ANP and BNP, can suppress the growth of cardiac fibroblasts and regulate the growth of cardiac tissue [ 8 , 26 ]. From midpregnancy onwards, the natriuretic peptide system appears to start its postnatal function and to be involved in the control of blood pressure and salt concentration via myocardial stress [ 8 ]. Thus, the prenatally increased NT-proBNP concentration may be explained as an expression of both, fetal cardiovascular maturation and high cardiac volume load in the fetal circulation. Thus, the decrease during the course of pregnancy could be explained by cardiac maturation and the decrease in left ventricular afterload [ 10 ]. The correlation of left ventricular volume load and NT-proBNP concentration is also observed in the cord blood of neonates in the first days of life [ 27 ]. Pathological elevation of NT-proBNP concentrations in fetal blood is associated with cardiovascular dysfunction of different causes [ 28 ]. The presence of anemia increases cardiac output due to decreased blood oxygen and leads to myocardial stress with activation of the natriuretic peptide system [ 29 ]. BNP in particular is thought to play a critical role in cardiac remodeling under hypoxic myocardial injury [ 25 ]. The present study considered the NT-proBNP concentration in anemic fetuses, focusing on those with Rhesus incompatibility and PVB19 infection, as well as in the status of cardiac decompensation in hydrops fetalis. Our results confirmed that NT-proBNP concentration is pathologically elevated in fetal anemia and increases with anemia severity (R=-0.64, p < 0.001), regardless of the cause of anemia. Fetuses with Rhesus incompatibility are known to have increased NT-proBNP concentrations in fetal blood [ 15 , 23 , 29 ]. In our study, fetuses with a PVB19 infection showed the highest NT-proBNP levels (see Fig. 2), whereas their MoM-Hb values and MoM-MCA-PSV values showed no significant difference compared to fetuses with Rhesus incompatibility (see Table 3 ). It has to be noticed, that the median of the first IUT was 6 weeks earlier in fetuses with PVB19 infection than in those with Rhesus incompatibility and we know that NT-proBNP levels decrease with progressing pregnancy (see Fig. 1). It could also be stated that fetuses with PVB19 infection suffer a more severe cardiac compromise than fetuses with Rhesus incompatibility at the same anemia severity. These results are in contrast to the work of Merz et al [ 12 ], who found no effect of PVB19 infection on NT-proBNP concentration (n = 8). The different results could be due to their smaller sample size. Further studies are needed, analyzing NT-proBNP concentration in the blood of fetuses with PVB19 infection, as no further studies could be found in our literature search. An explanation of the high NT-proBNP levels of PVB19 infected fetuses could be the associated PVB19 myocarditis, which results from viral infection of myocardial cells [ 30 – 32 ]. It has to be mentioned that in our cohort, there was a high prevalence of fetuses with hydrops fetalis in the PVB19 subgroup (62%), which is higher than in other reported studies with a prevalence of up to 24% [ 33 ]. This may have resulted from the selection of fetuses, as only fetuses requiring therapy were included. In addition, the average gestational age in the PVB19 subgroup was less than 20 weeks gestation, thus increasing the risk of hydrops fetalis [ 34 ]. In fetuses with PVB19 infection, the prevalence of hydrops fetalis is known to be high, even in less severe anemia, as PVB19 infection prevalence is high at earlier weeks of gestation, when diastolic and systolic cardiac function is still limited, and depending on the venous pressure, lead to hydrops more frequently [ 30 , 35 – 37 ]. Studies on NT-proBNP concentration in hydropic fetuses with PVB19 infection are not available. Fetal hydrops develops in fetuses with severe anemia (Hb < 4–7 g/dL), when compensatory mechanisms are exhausted [ 38 , 39 ]. An increased NT-proBNP concentration has already been demonstrated in fetuses with anemia when hydrops was present [ 12 ], which was also significantly shown in our results (see Fig. 2). Yarav et. al [ 29 ] presented high NT-proBNP concentrations in 10 hydropic fetuses with Rhesus incompatibility, showing an increasing concentration with increasing severity of hydrops fetalis. IUT therapy improves survival rates in fetuses with anemia, even though the cardiac load is temporarily increased by the transfused blood [ 40 ]. Walther et al. [ 23 ] showed a 13% short-term increase in NT-proBNP concentration during IUT and explained this by the transfusion-related volume load. Other studies showed a decrease in NT-proBNP concentration before subsequent IUTs in fetuses with rhesus incompatibility [ 15 , 29 ]. Merz et. al [ 12 ] further described a normalization of NT-proBNP concentration after three IUTs, while increased MCA-PSV and low Hb remained as signs of anemia (n = 27) Our results share this observation (see Fig. 3). Our use of reference values, which were calculated and adjusted for gestational age, increases the reliability of detecting pathological concentrations. Before the first IUT, only 5% of the measured NT-proBNP concentrations were within the reference range, after the third IUT, 64% of these values were within the reference range, while the measured MoM-MCA-PSV values and the MoM-Hb values remained pathological before each IUT (see Table 3 ). It appears that myocardial distress decreased, despite the transfused volume and the presence of anemia. A major factor was certainly the increase and transient normalization for a longer period in hemoglobin after transfusion. Although adult erythrocytes have a poorer oxygen-binding curve than fetal erythrocytes, the latter have a less rigid cell membrane and smaller volumes. In addition, a cardiac remodeling as an adaptation of fetal cardiomyocytes to the hypoxic state may have occurred [ 12 ]. In fetal sheep, an increase in myocardial mass and moycardial vascularization were observed during the course of anemia, reflecting the high adaptability of cardiomyocytes [ 41 ]. In accordance with the results of Merz et al. [ 12 ] and Luterek et al.[ 15 ] by using the specific GA-dependent reference values, our results show a decrease in NT-proBNP concentration and cardiac unloading during serial IUTs. Especially in an invasive therapy such as sequential IUT therapy, the implemented determination of NT-proBNP concentration may allow an assessment of the cardiac status and may help to detect the risk of developing hydrops fetalis due to cardiac decompensation in the future [ 16 ]. Conclusion NT-proBNP is an established biomarker for cardiac dysfunction used in adult and pediatric medicine and has been extended to fetal life. NT-proBNP concentrations is described to be distinctly higher in prenatal than in postnatal period. We could show, that the physiological concentration of this marker decreases with ongoing pregnancy and established GA-dependent normal values in cord blood. Anemia increases the workload of a fetal heart, so we found elevated concentrations in fetal blood, which correlated well with the degree of anemia. Highest levels of NT-proBNP values were found in cases with heart failure, shown by hydrops fetalis. For the same extent of anemia, PVB19-induced anemia showed higher NT-proBNP concentrations than Rhesus incompatibility, maybe due to a virus associated myocarditis, but also because PVB19-associated anemia was diagnosed at an earlier gestational age with higher levels per se. In both groups, IUT treatment resulted in a significant decrease of the NT-proBNP concentration, whereas Hb and MCA-PSV measurements remained abnormal. By indicating the extent of cardiac stress NT-proBNP may be a useful marker in management of fetal anemia and IUT monitoring, especially in cases at risk for hydrops fetalis. Declarations Author Contribution All authors contributed to the study conception and design. Material, preparation, data collection and analysis were performed by P. Siebers and E. Weber, who have written the first draft of the manuscript. All authors commented on previous versions, read and approved the final manuscript. P Siebers: Data Collection, Manuscript writing U Gembruch: Project development, Manuscript editing WM Merz: Project development, Manuscript editing F Recker: Data Collection, Manuscript editing A Müller: Manuscript editing B Strizek: Manuscript editing A Geipel: Manuscript editing C Berg: Manuscript editing EC Weber: Data Collection, Project development, Manuscript writing Compliance with Ethical Standards Funding: The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. Conflict of interest: The authors have no relevant financial or non-financial interests to disclose. Ethics approval: All procedures performed were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Approval was granted by the Ethics Committee of University of Bonn (Study ID 208/08). Consent to participate: Informed consent was obtained from all individual patients. References Nicolaides KH, Clewell WH, Mibashan RS, MEASUREMENT IN THE ASSESSMENT OF RED CELL ISOIMMUNISATION (1988) FETAL HAEMOGLOBIN. The Lancet 331:1073–1075. https://doi.org/10.1016/S0140-6736(88)91896-X Prefumo F, Fichera A, Fratelli N, Sartori E (2019) Fetal anemia: Diagnosis and management. Best Pract Res Clin Obstet Gynecol 58:2–14. https://doi.org/10.1016/j.bpobgyn.2019.01.001 Baschat AA, Muench MV, Gembruch U (2003) Coronary artery blood flow velocities in various fetal conditions: Fetal coronary blood flow. Ultrasound Obstet Gynecol 21:426–429. https://doi.org/10.1002/uog.82 Sohan K, Carroll SG, De La Fuente S et al (2001) Analysis of outcome in hydrops fetalis in relation to gestational age at diagnosis, cause and treatment: Hydrops fetalis. 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Neuro Endocrinol Lett 32:657–662 Merz WM, Gembruch U (2014) Old tool - new application: NT-proBNP in fetal medicine. Ultrasound Obstet Gynecol 44:377–385. https://doi.org/10.1002/uog.13443 Lechner E, Wiesinger-Eidenberger G, Wagner O et al (2009) Amino Terminal pro B-Type Natriuretic Peptide Levels Are Elevated in the Cord Blood of Neonates With Congenital Heart Defect. Pediatr Res 66:466–469. https://doi.org/10.1203/PDR.0b013e3181b3aee4 Leufgen C, Gembruch U, Stoffel-Wagner B et al (2017) N-terminal pro-B-type natriuretic peptide in amniotic fluid of fetuses with known or suspected cardiac load. PLoS ONE 12:e0177253. https://doi.org/10.1371/journal.pone.0177253 Oepkes D, Seaward PG, Vandenbussche FPHA et al (2006) Doppler ultrasonography versus amniocentesis to predict fetal anemia. N Engl J Med 355:156–164. https://doi.org/10.1056/NEJMoa052855 Detti L, Oz U, Guney I et al (2001) Doppler ultrasound velocimetry for timing the second intrauterine transfusion in fetuses with anemia from red cell alloimmunization. Am J Obstet Gynecol 185:1048–1051. https://doi.org/10.1067/mob.2001.118161 Bar-Oz B, Lev-Sagie A, Arad I et al (2005) N-terminal pro-B-type natriuretic peptide concentrations in mothers just before delivery, in cord blood, and in newborns. Clin Chem 51:926–927. https://doi.org/10.1373/clinchem.2005.048892 Fortunato G, Carandente Giarrusso P, Martinelli P et al (2006) Cardiac troponin T and amino-terminal pro-natriuretic peptide concentrations in fetuses in the second trimester and in healthy neonates. Clin Chem Lab Med (CCLM) 44. https://doi.org/10.1515/CCLM.2006.144 Walther T, Stepan H, Faber R (2001) Dual natriuretic peptide response to volume load in the fetal circulation. Cardiovasc Res 49:817–819. https://doi.org/10.1016/s0008-6363(00)00303-5 Seong WJ, Yoon DH, Chong GO et al (2010) Umbilical cord blood amino-terminal pro-brain natriuretic peptide levels according to the mode of delivery. Arch Gynecol Obstet 281:907–912. https://doi.org/10.1007/s00404-009-1253-3 Bakker J, Gies I, Slavenburg B et al (2004) Reference values for N-terminal pro-B-type natriuretic peptide in umbilical cord blood. Clin Chem 50:2465. https://doi.org/10.1373/clinchem.2004.040253 Swynghedauw B (1999) Molecular mechanisms of myocardial remodeling. Physiol Rev 79:215–262. https://doi.org/10.1152/physrev.1999.79.1.215 Schwachtgen L, Herrmann M, Georg T et al (2005) Reference values of NT-proBNP serum concentrations in the umbilical cord blood and in healthy neonates and children. Z Kardiol 94:399–404. https://doi.org/10.1007/s00392-005-0246-x Kocylowski RD, Dubiel M, Gudmundsson S et al (2009) Biochemical tissue-specific injury markers of the heart and brain in postpartum cord blood. Am J Obstet Gynecol 200. https://doi.org/10.1016/j.ajog.2008.10.009 . :273.e1-273.e25 Yadav V, Deka D, Aparna S, Dadhwal V (2019) NT-proBNP: A Useful Biochemical Marker for Prognosis in Rh-Isoimmunized Pregnancies. J Obstet Gynaecol India 69:128–132. https://doi.org/10.1007/s13224-018-1180-y Porter HJ, Quantrill AM, Fleming KA (1988) B19 parvovirus infection of myocardial cells. Lancet 1:535–536. https://doi.org/10.1016/s0140-6736(88)91332-3 Young NS, Brown KE (2004) Parvovirus B19. N Engl J Med 350:586–597. https://doi.org/10.1056/NEJMra030840 Girsen A, Ala-Kopsala M, Mäkikallio K et al (2007) Cardiovascular hemodynamics and umbilical artery N-terminal peptide of proB-type natriuretic peptide in human fetuses with growth restriction. Ultrasound Obstet Gynecol 29:296–303. https://doi.org/10.1002/uog.3934 Heegaard ED, Brown KE (2002) Human parvovirus B19. Clin Microbiol Rev 15:485–505. https://doi.org/10.1128/CMR.15.3.485-505.2002 Enders M, Klingel K, Weidner A et al (2010) Risk of fetal hydrops and non-hydropic late intrauterine fetal death after gestational parvovirus B19 infection. J Clin Virol 49:163–168. https://doi.org/10.1016/j.jcv.2010.07.014 Morey AL, Nicolini U, Welch CR et al (1991) Parvovirus B19 infection and transient fetal hydrops. Lancet 337:496. https://doi.org/10.1016/0140-6736(91)93435-c Forestier F, Tissot JD, Vial Y et al (1999) Haematological parameters of parvovirus B19 infection in 13 fetuses with hydrops foetalis. Br J Haematol 104:925–927. https://doi.org/10.1046/j.1365-2141.1999.01241.x Cosmi E, Mari G, Delle Chiaie L et al (2002) Noninvasive diagnosis by Doppler ultrasonography of fetal anemia resulting from parvovirus infection. Am J Obstet Gynecol 187:1290–1293. https://doi.org/10.1067/mob.2002.128024 Pasman SA, van den Brink CPB, Kamping MA et al (2009) Total blood volume is maintained in nonhydropic fetuses with severe hemolytic anemia. Fetal Diagn Ther 26:10–15. https://doi.org/10.1159/000236353 van Kamp IL, Klumper FJ, Bakkum RS et al (2001) The severity of immune fetal hydrops is predictive of fetal outcome after intrauterine treatment. Am J Obstet Gynecol 185:668–673. https://doi.org/10.1067/mob.2001.116690 Zwiers C, Lindenburg ITM, Klumper FJ et al (2017) Complications of intrauterine intravascular blood transfusion: lessons learned after 1678 procedures. Ultrasound Obstet Gynecol 50:180–186. https://doi.org/10.1002/uog.17319 Jonker SS, Giraud MK, Giraud GD et al (2010) Cardiomyocyte enlargement, proliferation and maturation during chronic fetal anaemia in sheep. Exp Physiol 95:131–139. https://doi.org/10.1113/expphysiol.2009.049379 Cite Share Download PDF Status: Published Journal Publication published 26 Mar, 2023 Read the published version in Archives of Gynecology and Obstetrics → Version 1 posted Reviewers agreed at journal 09 Jan, 2023 Reviewers invited by journal 14 Dec, 2022 Editor invited by journal 12 Dec, 2022 Editor assigned by journal 12 Dec, 2022 First submitted to journal 10 Dec, 2022 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2347669","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":160033560,"identity":"631e00cc-cc9a-4dd4-b7b7-404dd6460c72","order_by":0,"name":"Pauline Siebers","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Pauline","middleName":"","lastName":"Siebers","suffix":""},{"id":160033561,"identity":"4bd8e34f-e0ab-459f-939c-939c3b3d0015","order_by":1,"name":"Ulrich 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version.\u003c/p\u003e","description":"","filename":"OnlineKontrollen.png","url":"https://assets-eu.researchsquare.com/files/rs-2347669/v1/3d05b946ad717134dc2fb600.png"},{"id":30437940,"identity":"3d9799d5-93d3-41b1-b305-a6a69801daf8","added_by":"auto","created_at":"2022-12-16 16:26:42","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":8873,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not included with this version.\u003c/p\u003e","description":"","filename":"OnlineGruppenVorIUT.png","url":"https://assets-eu.researchsquare.com/files/rs-2347669/v1/041996bd64aec77edbb45015.png"},{"id":30437942,"identity":"02464a3c-91e8-4f37-8599-3c746badf009","added_by":"auto","created_at":"2022-12-16 16:26:42","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":11604,"visible":true,"origin":"","legend":"\u003cp\u003eLegend not included with this version.\u003c/p\u003e","description":"","filename":"OnlineIUTVerlauf.png","url":"https://assets-eu.researchsquare.com/files/rs-2347669/v1/661be0b9f22be8cfca92745e.png"},{"id":44723580,"identity":"9c6553bd-e9a3-4714-bf57-b9082024c981","added_by":"auto","created_at":"2023-10-16 20:16:48","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":322957,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2347669/v1/13e1f0db-66e0-4e11-ae8c-4e52108537b0.pdf"}],"financialInterests":"","formattedTitle":"Fetal NT-proBNP levels and their course in severe anemia during intrauterine treatment","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSevere anemia of the fetus is defined as low cord blood concentration of haemoglobin (Hb) more than 7–10 g/dl below the mean for gestational age [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Causes can be immunological (alloimmunization), such as Rhesus incompatibility, or non-immunological, such as PVB19 infections. Ultrasound findings signalling hydrops fetalis (skin edema, ascites, hydrothorax, cardiomegaly, placentomegaly, polyhydramnios) and an increased peak systolic velocity of the middle cerebral artery (MCA-PSV), measured by Doppler ultrasound, lead to the diagnosis [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Fetal anemia causes increased cardiac output and hyperdynamic circulatory adaptions, such as increased myocardial stretching, wall stress and filling pressures that cause cardiac remodelling and cardiomegaly. In fetuses with severe anemia, a marked increase in coronary perfusion can be demonstrated by Doppler echocardiography [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Coronary perfusion of the hypertrophic myocardium may increase up to fivefold, but when those adapting mechanisms are exhausted, myocardial ischemia occurs. Severe fetal anemia can cause heart failure with hydrops, as the fetal compartiments react sensitively to circulatory stress and intrauterine demise becomes imminent [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eN-terminal pro-B-type (NT-proBNP) is a marker of cardiac dysfunction and myocardial remodelling, known in adult [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], as well as fetal medicine [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Its circulating levels correlate with myocardial wall stress, cardiac workload and an increased central venous pressure [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In the fetus, the natriuretic system, which regulates blood-pressure by diuresis and vasodilatation, starts at mid-gestation [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Various studies presented normal values for newborns and children [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] but only very few report on the circulating concentration prenatally [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Increased NT-proBNP levels have been presented in fetuses with cardiovascular dysfunctions, such as structural cardiac malformations [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], as well as in fetuses with anemia [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], but also in fetuses with urinary tract malformations [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] or severe growth restriction [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Few studies have presented NT-proBNP values during treatment with intrauterine transfusions [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHaving doubled our numbers over the past decade, in this study, we aimed to update information on fetal NT-proBNP values, stating normal values during pregnancies of fetuses without increased cardiac load, and comparing those to anemic fetuses during treatment with serial intrauterine transfusions.\u003c/p\u003e "},{"header":"Methods","content":"\u003cp\u003eThis retrospective study included all fetuses receiving intrauterine transfusion (IUT) (subjects) between March 2009 and October 2020 and fetuses that underwent feticide by intravascular injection of potassium chloride, without a suspected disease that could influence fetal NT-proBNP levels (controls) between January 2017 and October 2020 at the tertiary center for Prenatal Medicine of the University of Bonn. In our center we perform about 50 IUTs and 100 feticides annually. Ethical approval was achieved by the Ethics Committee of the University of Bonn.\u003c/p\u003e\u003cp\u003eAll fetuses underwent a detailed scan, using high-resolution ultrasound equipment, before each puncture (each IUT and feticide), including Doppler sonographic measurements of the arteria umbilicalis, ductus venosus and MCA. To assess fetal anemia the MCA-PSV was measured, with an insonation angle of \u0026lt; 10° and calculated in multiples of the median (MoM) by the formula e\u003csup\u003e(2.31+0.046/GA)\u003c/sup\u003e. Hb values were determined before transfusion or feticide and were converted to MoM-Hb values. A MoM-Hb value of 0.84 − 0.65 indicated mild anemia, MoM-Hb values of 0.64 − 0.55 moderate anemia, and MoM-Hb values of \u0026lt; 0.55 indicated severe anemia. In each case, we sought for reasons of fetal anemia. When Coombs test of maternal blood showed a titer of \u0026gt; 1:32 for Rhesus-antibodies (CcDEe), Rhesus incompatibility was diagnosed. PVB19 infection was confirmed either by PCR of fetal blood/amniotic fluid or by maternal IgM antibodies and sonographic signs for severe anemia. Hydrops fetalis was diagnosed when at least two of the following signs were present, including at least one fetal compartiment: ascites, hydrothorax, pericardial effusion, skin edema, and placentomegaly, cardiomegaly or polyhydramnios. Intrauterine growth restriction (IUGR) was defined as an estimated fetal weight percentile \u0026lt; 10%. The following parameters were analyzed from the fetal blood samples: NT-proBNP (pg/ml) and haemoglobin (g/dl). We assessed the gestational age at first presentation at our center, at the puncture (each IUT and feticide) and outcome measures. All fetuses that underwent serial IUTs due to anemia belonged to this group. We excluded anemic fetuses with growth restriction before the first IUT. 10 fetuses in this group have been described in a previous publication [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. For the puncture we used a 22G-needle, which was guided into the umbilical vein by ultrasound.\u003c/p\u003e\u003cp\u003eSubjects: Fetal blood sampling was initiated, followed by the IUT. To avoid volume overload, we applied no more than 30-50ml per kilogram estimated fetal weight (without hydrops), using cross-matched, 0 Rhesus-negative and cytomegaly virus-negative, irradiated packed red blood cells. In cases of severe anemia we performed a subsequent IUT 2–5 days later if the haemoglobin concentration was below 10g/dl at the end of IUT. Follow-up ultrasound and Doppler scans were achieved on the next day, followed by weekly scans. We collected the number of performed IUTs and the interval between IUTs.\u003c/p\u003e\u003cp\u003eControls: Feticide was performed according to the national legislation, and all fetuses offering conditions that may influence the blood levels of NT-proBNP were excluded, such as cardiovascular dysfunctions (cardiac or thoracic malformations, infections, hydrops), urinary tract malformations, tumors, neuromuscular disorders, growth restriction, pathological Doppler assessment (high resistance in the umbilical artery or ductus venosus) and monochorionic multiple pregnancies. For feticide, the umbilical vein was punctured by a 22G-needle under ultrasound control and before injection of the potassium chloride, fetal blood was withdrawn for analysis. Fetuses with proven anemia in the blood sample or with suspected anemia, showing increased MCA-PSV were excluded from the control group.\u003c/p\u003e\u003cp\u003eAll examined values were tested for normal distribution using the Kolmogorov-Smirnov test. Parameters showing positive skewness, such as NT-proBNP concentration, were considered logarithmized. The following influences on blood analysis variables in the control group were examined using multiple linear regressions: Child sex and disease, maternal BMI and age and gestational age. All requirements for a multiple linear regression were met; residuals were tested for normal distribution using the Shapiro-Wilk test. For comparison of means between subgroups, analysis of variance (ANOVA) and the Bonnferoni post-hoc test as well as the Games-Howell post-hoc test were performed. Linear correlations within groups were estimated with the Pearson correlation coefficient. The course of blood test results of sequential IUTs was explored using a linear mixed model. The significance level was set at p \u0026lt; 0.05 for each analysis. We used IBM SPSS Statistics 27.0 for data analyses.\u003c/p\u003e\u003cp\u003eWe analyzed the normal blood values of NT-proBNP in fetuses that underwent feticide and not showing any signs or diseases that could affect the natriuretic system and compared our results to the norm values of Merz et al [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Comparing controls and subjects, we analyzed the effect of anemia and the IUT-therapy on the NT-proBNP-level. Within the anemic group we performed two subanalyses. First, we analyzed if there were differences in the circulating NT-proBNP levels, comparing cases with Rhesus incompatibility with those affected by a PVB19 infection and the influence of the diagnosis of fetuses with hydrops. Second, we analyzed the course of the NT-proBNP levels during serial IUT therapy.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e86 fetuses, whose blood samples were taken during feticide, presented the control group. 190 feticides had to be excluded, as the fetuses presented with diagnoses that might have had an impact on NT-proBNP levels. Reasons for feticide are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The subject group consisted of 183 fetuses, which received IUT. We excluded 63 monochorionic twin pregnancies, 3 triplets and 10 IUGRs, leaving n\u0026thinsp;=\u0026thinsp;107 for analysis. Reasons for fetal anemia are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. 54 subjects showed hydrops fetalis and were investigated as a subgroup. 41 fetuses had Rhesus incompatibility and 29 a PVB19 infection.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDiagnosed diseases in the group of controls and subjects Data in number n (%)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003eDisease\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eControls\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eSubjects\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNumber of hydropic fetuses\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSkeletal dysplasia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5 (5.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRhesus incompatibility\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e41 (38.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15/41 (36.6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNeural tube defects\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15 (17.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eParvovirus B19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e29 (27.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18/29 (62.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBrain Malformations\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e39 (45.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eKell anemia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8 (7.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4/8 (50.0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTrisomy 21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14 (16.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCytomegaly virus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3 (2.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3/3 (100.0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChromosomal aberrations\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2 (2.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eChorangioma\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3 (2.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1/3 (33.3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eDiverse\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e11 (12.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHomozygotic alpha-Thalassemia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1 (0.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1 (100.0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCongenital dyserythropoetic anemia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1 (0.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTrisomy 21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1 (0.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1 (100.0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAnemia for other or unknown etiology\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20 (18.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11 (55.0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTotal\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e86 (100)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e107 (100)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e54/107 (50.0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe median interval between the first and the second IUT was 7 days (n\u0026thinsp;=\u0026thinsp;107, SD\u0026thinsp;=\u0026thinsp;0.70), and 13 days between the second and the third IUT (n\u0026thinsp;=\u0026thinsp;84, SD\u0026thinsp;=\u0026thinsp;1.05). Of the 107 fetuses that underwent serial IUT, 91 were born alive at a median gestational age of 35.1weeks (SD\u0026thinsp;=\u0026thinsp;3.7) and a birth weight of 2692\u0026thinsp;\u0026plusmn;\u0026thinsp;724 on a centile of 49\u0026thinsp;\u0026plusmn;\u0026thinsp;27. Eleven subjects suffered intrauterine fetal death (IUD). Seven of these fetuses had a PVB19 infection with severe hydrops fetalis. Of those eleven IUDs, five occurred within 24 hours after the transfusion. Five children died postnatally. In all of these neonatal deaths (NND), hydrops fetalis was diagnosed during pregnancy. Two of them were delivered at 27 weeks with severe anemia of unknown cause, one at 28 weeks with CMV infection, one at 32 weeks with trisomy 21 and one at 21 weeks with multiple chroangiomata. In five cases, no information on the outcome could be collected.\u003c/p\u003e \u003cp\u003eBaseline characteristics, Doppler measurements and blood parameters of subjects and controls, as well as the subgroups Rhesus incompatibility and PVB19 are listed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Maternal age and body mass index (BMI) as well as the distribution of the fetal sex were comparable in the groups.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBasic characteristics and measurements of the patient collective\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSubjects\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;107\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSubgroup \u003c/p\u003e \u003cp\u003eRhesus\u003c/p\u003e \u003cp\u003eIncompatibility\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;41\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSubgroup PVB19\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;29\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eControls\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;86\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003eMaternal characteristics\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge mother [years]\u003csub\u003ea\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31.4\u0026thinsp;\u0026plusmn;\u0026thinsp;5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e31.2\u0026thinsp;\u0026plusmn;\u0026thinsp;5.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e31.4\u0026thinsp;\u0026plusmn;\u0026thinsp;5.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBMI mother [kg/m\u0026sup2;] \u003csub\u003ea\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26.1\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27.1\u0026thinsp;\u0026plusmn;\u0026thinsp;4.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e26.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e27.8\u0026thinsp;\u0026plusmn;\u0026thinsp;5.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGravidity of the mother \u003csub\u003ea\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMother parity \u003csub\u003ea\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGA at first intervention [week, days] \u003csub\u003ea\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23.6\u0026thinsp;\u0026plusmn;\u0026thinsp;6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25.3\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.0\u0026thinsp;\u0026plusmn;\u0026thinsp;3.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFetal characteristics\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale fetuses \u003csub\u003eb\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e51 (47.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22 (53.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15 (51.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e38 (44.2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemale fetuses \u003csub\u003eb\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e53 (49.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17 (41.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14 (48.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e48 (55.8)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDichorionic twins \u003csub\u003eb\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5 (4.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2 (4.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1 (3.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5 (5.8)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEstimated weight [g] \u003csub\u003ea\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e843\u0026thinsp;\u0026plusmn;\u0026thinsp;627\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1081\u0026thinsp;\u0026plusmn;\u0026thinsp;664\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e356\u0026thinsp;\u0026plusmn;\u0026thinsp;145\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e704\u0026thinsp;\u0026plusmn;\u0026thinsp;442\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHydrops fetalis \u003csub\u003eb\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e54 (50.5)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15 (36.6)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18 (62.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eOutcome\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLive births \u003csub\u003eb\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e91 (80.4)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37 (90.2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e22 (75.9)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBirth weight (BW) [g] \u003csub\u003ea\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2692\u0026thinsp;\u0026plusmn;\u0026thinsp;724\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2658\u0026thinsp;\u0026plusmn;\u0026thinsp;584\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2950\u0026thinsp;\u0026plusmn;\u0026thinsp;1078\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePercentile of BW \u003csub\u003eb\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e49\u0026thinsp;\u0026plusmn;\u0026thinsp;27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e53\u0026thinsp;\u0026plusmn;\u0026thinsp;27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e36\u0026thinsp;\u0026plusmn;\u0026thinsp;25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIntrauterine death (IUD) \u003csub\u003ea\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11(10.3)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7 (24.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo information \u003csub\u003eb\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5 (4.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4 (9.7)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csub\u003ea\u003c/sub\u003e Data in mean (M)\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csub\u003eb\u003c/sub\u003e Data in number n (%)\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe NT-proBNP concentration in the control group showed a mean of 1339\u0026thinsp;\u0026plusmn;\u0026thinsp;639 pg/ml. There was a significant decline in NT-proBNP concentration with advancing gestational age (p\u0026thinsp;=\u0026thinsp;0.001), showing an average decrease of 74 pg/ml per week of gestation. Overall, the mean dropped from 1813 pg/ml at 19 weeks to 702 pg/ml at week 34 (see Fig.\u0026nbsp;1). There was one outlier in the group with a NT-proBNP value of 4413 pg/ml. This fetus had a normal Hb and was not anemic. Feticide was performed for open spina bifida. The different fetal diagnoses, maternal age and BMI showed no influence on NT-proBNP concentration in the multiple linear regression (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). Only male sex showed a slightly increased NT-proBNP concentration compared to the female sex (p\u0026thinsp;=\u0026thinsp;0.006, β\u0026thinsp;=\u0026thinsp;0,34, R\u0026thinsp;=\u0026thinsp;431). However, the strength of this influence was lower, measured by standardized coefficient ((β)\u0026thinsp;=\u0026thinsp;0.3), than the influence of gestational age (β\u0026thinsp;=\u0026thinsp;0.5).\u003c/p\u003e \u003cp\u003eIn the group of subjects, there was a strong correlation between the severity of fetal anemia (MoM-Hb) and both, NT-proBNP values (R=-0.64, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) as well as MoM-MCA-PSV values (R=-0.50, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). ANOVA showed significant differences in the NT-proBNP levels (F\u0026thinsp;=\u0026thinsp;48.5, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), MoM-Hb values (F\u0026thinsp;=\u0026thinsp;81.62, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and MoM-MCA-PSV values (F\u0026thinsp;=\u0026thinsp;68.81 p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), comparing controls and subjects, subgroups of fetuses with PVB19 infection and fetuses with Rhesus incompatibility as well as fetuses with and without hydrops fetalis in the fetal blood before the start of therapy, compared to the controls at the time of feticide (see Fig.\u0026nbsp;2). The subgroup of anemic fetuses with PVB19 infection showed the highest blood levels of NT-proBNP concentration, compared to the control group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and compared to the subgroup of Rhesus incompatibility (p\u0026thinsp;=\u0026thinsp;0.026) (see Fig.\u0026nbsp;2). But the mean value of fetuses with Rhesus incompatibility was also significantly higher compared to the control group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). MoM-MCA (p\u0026thinsp;=\u0026thinsp;0.330) and MoM-Hb levels (p\u0026thinsp;=\u0026thinsp;0.892) did not show a significant difference between fetuses of Rhesus incompatibility and fetuses with PVB19 infection. Moreover, fetuses with hydrops showed significantly higher NT-proBNP levels compared to anemic fetuses without hydrops (p\u0026thinsp;=\u0026thinsp;0.006), and also compared to controls (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Before the start of therapy, subjects with hydrops fetalis showed a mean NT-proBNP concentration of 21959\u0026thinsp;\u0026plusmn;\u0026thinsp;219959 pg/ml, whereas fetuses without hydrops showed a mean of 52946\u0026thinsp;\u0026plusmn;\u0026thinsp;54777 pg/ml. Those observations could also be made for MoM-Hb (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and MoM-MCA (p\u0026thinsp;=\u0026thinsp;0.049) when comparing the hydropic fetuses to non-hydropic fetuses.\u003c/p\u003e \u003cp\u003eDuring therapy, NT-proBNP (β=-0.14, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, 95%CI=-0.17 to -0.11) and MoM-MCA-PSV (β=-0.09, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, 95%CI=-1.1 to -0.07)) values significantly decreased, while the MoM-Hb (β\u0026thinsp;=\u0026thinsp;0.05, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, 95%CI\u0026thinsp;=\u0026thinsp;0.04 to 0.06) values significantly increased (see Fig.\u0026nbsp;3 and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The greatest change in all parameters occurred between the first and second transfusion. The median of NT-proBNP decreased 47% between the first and second IUT (95%CI=-63% to -31%) and 36% between the second and third IUT (95%CI=-62% to -10%). Based on the GA-dependent values obtained, only 5% of the measured NT-proBNP concentrations were within the physiological range before the first IUT. After the third IUT, it was 63% of the measured values (n\u0026thinsp;=\u0026thinsp;14). Thus, more fetuses had physiological NT-proBNP concentrations than pathological NT-proBNP concentrations. MoM-Hb values increased from a median of 0.42 (Q1-Q3\u0026thinsp;=\u0026thinsp;0.24\u0026ndash;0.58) to a median of 0.78 (Q1-Q3\u0026thinsp;=\u0026thinsp;0.55\u0026ndash;0.84) from first to second IUT. MoM-MCA-PSV values decreased from a median of 2.12 (Q1-Q3\u0026thinsp;=\u0026thinsp;1.78\u0026ndash;2.36) to 1.59 (Q1-Q3\u0026thinsp;=\u0026thinsp;1.33\u0026ndash;1.95) from first to second IUT. Overall, levels of MoM-MCA-PSV and MoM-Hb remained pathological before each transfusion. See Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e for the measured values before each IUT.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMeasurements of different parameters in controls subjects and subgroups before feticide (FC) (controls) or each intrauterine transfusion (IUT) (subjects).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNT-proBNP [pg/ml]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMoM-MCA-PSV\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMoM-Hb\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eControls\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1399\u0026thinsp;\u0026plusmn;\u0026thinsp;639 [58]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21 [63]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.04\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10 [54]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eIUT 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSubjects\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;107\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37452\u0026thinsp;\u0026plusmn;\u0026thinsp;44205 [54]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42 [107]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21 [100]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRhesus Incompatibility\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27937\u0026thinsp;\u0026plusmn;\u0026thinsp;37680 [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.05\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42 [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21 [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePVB19\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e46420\u0026thinsp;\u0026plusmn;\u0026thinsp;36982 [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.39 [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20 [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eIUT 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSubjects\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28490\u0026thinsp;\u0026plusmn;\u0026thinsp;57721[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.41 [80]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18 [79]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRhesus Incompatibility\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9366\u0026thinsp;\u0026plusmn;\u0026thinsp;14261 [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.59\u0026thinsp;\u0026plusmn;\u0026thinsp;0.36 [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21 [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePVB19\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33677\u0026thinsp;\u0026plusmn;\u0026thinsp;20504 [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.39 [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18 [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eIUT 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSubjects\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6453\u0026thinsp;\u0026plusmn;\u0026thinsp;7793 [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.60\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35 [56]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20 [52]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRhesus Incompatibility\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5078\u0026thinsp;\u0026plusmn;\u0026thinsp;6336 [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.59\u0026thinsp;\u0026plusmn;\u0026thinsp;0.40 [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20 [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePVB19\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22603\u0026thinsp;\u0026plusmn;\u0026thinsp;16249 [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.36 [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12 [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eIUT 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSubjects\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6710\u0026thinsp;\u0026plusmn;\u0026thinsp;11933 [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.59\u0026thinsp;\u0026plusmn;\u0026thinsp;0.44 [44]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.19 [43]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRhesus Incompatibility\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7882\u0026thinsp;\u0026plusmn;\u0026thinsp;14152 [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.60\u0026thinsp;\u0026plusmn;\u0026thinsp;0.50 [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21 [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eValues in mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD [measured values]\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eAuthor Contribution\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eAll authors contributed to the study conception and design. Material, preparation, data collection and analysis were performed by P. Siebers and E. Weber, who have written the first draft of the manuscript. All authors commented on previous versions, read and approved the final manuscript.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eP Siebers: Data Collection, Manuscript writing\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eU Gembruch: Project development, Manuscript editing\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eWM Merz: Project development, Manuscript editing\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eF Recker: Data Collection, Manuscript editing\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eA M\u0026uuml;ller: Manuscript editing\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eB Strizek: Manuscript editing\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eC Berg: Manuscript editing\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eEC Weber: Data Collection, Project development, Manuscript writing\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThroughout the course of IUT therapy, the differences in parameters described at the beginning remained (see Fig.\u0026nbsp;3). Hydropic fetuses showed higher levels of NT-proBNP in the cord-blood than non-hydropic fetuses (β\u0026thinsp;=\u0026thinsp;0.34, p\u0026thinsp;=\u0026thinsp;0.001, 95%CI\u0026thinsp;=\u0026thinsp;0.54 to 0.15). MoM-Hb-values were significantly lower during IUT-therapy in hydropic fetuses (\u0026szlig;=-0.11, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, 95%CI\u0026thinsp;=\u0026thinsp;0.06 to 0.17). Only MoM-MCA-PSV did not show significant differences during therapy (p\u0026thinsp;=\u0026thinsp;0.279). Fetuses with PVB19 infection showed significantly higher NT-proBNP levels compared to fetuses with Rhesus incompatibility during the first three IUTs (\u0026szlig;=0.58, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, 95%CI\u0026thinsp;=\u0026thinsp;0.88 to 0.27).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eBecause of its long half-life and high thermostability, NT-proBNP is an established marker for cardiac function in adults. In contrast to image-based diagnostics, there is no inter- or intraobserver variability. The correlation between cardiac stress and NT-proBNP concentration also appears to be strong in the fetal organism [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Although MCA-PSV measurement shows high reliability for anemia diagnosis, it cannot reliably predict the occurrence of hydrops fetalis [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] and the severity of cardiac compromise and is affected during IUT therapy by transfused adult erythrocytes [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePhysiological reference values of NT-proBNP concentration in fetal blood are difficult to define due to ethical considerations of the invasive procedure and different analytical methods [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. So far, there are only very few studies that deal with this topic. Fortunato et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] performed blood sampling in a cohort of 22 fetuses in the second trimester. The mean NT-proBNP concentration was 2308 pg/ml. Exclusion criteria were multiple pregnancies, severe fetal anomalies, and abnormal karyotypes. Walther et al. [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] calculated an average NT-proBNP concentration of 1052\u0026thinsp;\u0026plusmn;\u0026thinsp;182 pg/ml in the fetal blood of 9 fetuses. Blood samples were taken on the suspicion of fetal infection in the second trimester, which was not confirmed in the blood analysis. Both studies had a small number of cases and were limited to values before the 25 week of gestation. Merz et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] determined a mean NT-proBNP concentration in 59 fetuses of 1998 pg/ml (\u0026plusmn;\u0026thinsp;2SD\u0026thinsp;=\u0026thinsp;242\u0026ndash;3754) between 20 and 34 weeks of gestation. Exclusion criteria included structural malformations of the cardiovascular and urogenital systems and conditions with potential influence on NT-proBNP concentration. In our study, the average measured NT-proBNP concentration was 1339\u0026thinsp;\u0026plusmn;\u0026thinsp;639 pg/ml between 20 and 35 weeks' gestation (n\u0026thinsp;=\u0026thinsp;58), so it correlates with the previous data, using the same analytical procedure. Besides Merz et al. our results represent the largest sample size for normal NT-proBNP values in accordance to gestational age up to 35 weeks of gestation. Our regression analysis showed a significant decrease in NT-proBNP concentration with increasing gestational age (-74.04*GA\u0026thinsp;+\u0026thinsp;3220 pg/ml, p\u0026thinsp;=\u0026thinsp;0.001), which correlates well to the regression calculated by Merz et al. (-74.8*GA\u0026thinsp;+\u0026thinsp;3946 pg/ml, p\u0026thinsp;=\u0026thinsp;0.012) (see Fig.\u0026nbsp;1). NT-proBNP concentrations in umbilical cord samples in term pregnancies are significantly lower than values measured in the second trimester [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCompared to adult reference values (0\u0026ndash;10 pg/ml) and NT-proBNP blood concentration of pregnant women, fetal blood levels are significantly higher. Placental exchange during pregnancy and lack of renal elimination were excluded as causes [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The higher NT-proBNP concentration appears to result from intrinsic fetal production of this hormone [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Natriuretic peptides are involved in the development of various organ systems during the fetal period and are mainly responsible for the growth of cardiovascular tissue. Animal experiments have shown that both, ANP and BNP, can suppress the growth of cardiac fibroblasts and regulate the growth of cardiac tissue [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. From midpregnancy onwards, the natriuretic peptide system appears to start its postnatal function and to be involved in the control of blood pressure and salt concentration via myocardial stress [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Thus, the prenatally increased NT-proBNP concentration may be explained as an expression of both, fetal cardiovascular maturation and high cardiac volume load in the fetal circulation. Thus, the decrease during the course of pregnancy could be explained by cardiac maturation and the decrease in left ventricular afterload [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The correlation of left ventricular volume load and NT-proBNP concentration is also observed in the cord blood of neonates in the first days of life [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Pathological elevation of NT-proBNP concentrations in fetal blood is associated with cardiovascular dysfunction of different causes [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The presence of anemia increases cardiac output due to decreased blood oxygen and leads to myocardial stress with activation of the natriuretic peptide system [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. BNP in particular is thought to play a critical role in cardiac remodeling under hypoxic myocardial injury [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The present study considered the NT-proBNP concentration in anemic fetuses, focusing on those with Rhesus incompatibility and PVB19 infection, as well as in the status of cardiac decompensation in hydrops fetalis. Our results confirmed that NT-proBNP concentration is pathologically elevated in fetal anemia and increases with anemia severity (R=-0.64, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), regardless of the cause of anemia. Fetuses with Rhesus incompatibility are known to have increased NT-proBNP concentrations in fetal blood [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn our study, fetuses with a PVB19 infection showed the highest NT-proBNP levels (see Fig.\u0026nbsp;2), whereas their MoM-Hb values and MoM-MCA-PSV values showed no significant difference compared to fetuses with Rhesus incompatibility (see Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). It has to be noticed, that the median of the first IUT was 6 weeks earlier in fetuses with PVB19 infection than in those with Rhesus incompatibility and we know that NT-proBNP levels decrease with progressing pregnancy (see Fig.\u0026nbsp;1). It could also be stated that fetuses with PVB19 infection suffer a more severe cardiac compromise than fetuses with Rhesus incompatibility at the same anemia severity. These results are in contrast to the work of Merz et al [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], who found no effect of PVB19 infection on NT-proBNP concentration (n\u0026thinsp;=\u0026thinsp;8). The different results could be due to their smaller sample size. Further studies are needed, analyzing NT-proBNP concentration in the blood of fetuses with PVB19 infection, as no further studies could be found in our literature search. An explanation of the high NT-proBNP levels of PVB19 infected fetuses could be the associated PVB19 myocarditis, which results from viral infection of myocardial cells [\u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIt has to be mentioned that in our cohort, there was a high prevalence of fetuses with hydrops fetalis in the PVB19 subgroup (62%), which is higher than in other reported studies with a prevalence of up to 24% [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. This may have resulted from the selection of fetuses, as only fetuses requiring therapy were included. In addition, the average gestational age in the PVB19 subgroup was less than 20 weeks gestation, thus increasing the risk of hydrops fetalis [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. In fetuses with PVB19 infection, the prevalence of hydrops fetalis is known to be high, even in less severe anemia, as PVB19 infection prevalence is high at earlier weeks of gestation, when diastolic and systolic cardiac function is still limited, and depending on the venous pressure, lead to hydrops more frequently [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan additionalcitationids=\"CR36\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Studies on NT-proBNP concentration in hydropic fetuses with PVB19 infection are not available.\u003c/p\u003e \u003cp\u003eFetal hydrops develops in fetuses with severe anemia (Hb\u0026thinsp;\u0026lt;\u0026thinsp;4\u0026ndash;7 g/dL), when compensatory mechanisms are exhausted [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. An increased NT-proBNP concentration has already been demonstrated in fetuses with anemia when hydrops was present [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], which was also significantly shown in our results (see Fig.\u0026nbsp;2). Yarav et. al [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] presented high NT-proBNP concentrations in 10 hydropic fetuses with Rhesus incompatibility, showing an increasing concentration with increasing severity of hydrops fetalis.\u003c/p\u003e \u003cp\u003eIUT therapy improves survival rates in fetuses with anemia, even though the cardiac load is temporarily increased by the transfused blood [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. Walther et al. [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] showed a 13% short-term increase in NT-proBNP concentration during IUT and explained this by the transfusion-related volume load. Other studies showed a decrease in NT-proBNP concentration before subsequent IUTs in fetuses with rhesus incompatibility [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Merz et. al [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] further described a normalization of NT-proBNP concentration after three IUTs, while increased MCA-PSV and low Hb remained as signs of anemia (n\u0026thinsp;=\u0026thinsp;27) Our results share this observation (see Fig.\u0026nbsp;3). Our use of reference values, which were calculated and adjusted for gestational age, increases the reliability of detecting pathological concentrations. Before the first IUT, only 5% of the measured NT-proBNP concentrations were within the reference range, after the third IUT, 64% of these values were within the reference range, while the measured MoM-MCA-PSV values and the MoM-Hb values remained pathological before each IUT (see Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). It appears that myocardial distress decreased, despite the transfused volume and the presence of anemia. A major factor was certainly the increase and transient normalization for a longer period in hemoglobin after transfusion. Although adult erythrocytes have a poorer oxygen-binding curve than fetal erythrocytes, the latter have a less rigid cell membrane and smaller volumes. In addition, a cardiac remodeling as an adaptation of fetal cardiomyocytes to the hypoxic state may have occurred [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. In fetal sheep, an increase in myocardial mass and moycardial vascularization were observed during the course of anemia, reflecting the high adaptability of cardiomyocytes [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. In accordance with the results of Merz et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] and Luterek et al.[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] by using the specific GA-dependent reference values, our results show a decrease in NT-proBNP concentration and cardiac unloading during serial IUTs.\u003c/p\u003e \u003cp\u003eEspecially in an invasive therapy such as sequential IUT therapy, the implemented determination of NT-proBNP concentration may allow an assessment of the cardiac status and may help to detect the risk of developing hydrops fetalis due to cardiac decompensation in the future [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eNT-proBNP is an established biomarker for cardiac dysfunction used in adult and pediatric medicine and has been extended to fetal life. NT-proBNP concentrations is described to be distinctly higher in prenatal than in postnatal period. We could show, that the physiological concentration of this marker decreases with ongoing pregnancy and established GA-dependent normal values in cord blood. Anemia increases the workload of a fetal heart, so we found elevated concentrations in fetal blood, which correlated well with the degree of anemia. Highest levels of NT-proBNP values were found in cases with heart failure, shown by hydrops fetalis. For the same extent of anemia, PVB19-induced anemia showed higher NT-proBNP concentrations than Rhesus incompatibility, maybe due to a virus associated myocarditis, but also because PVB19-associated anemia was diagnosed at an earlier gestational age with higher levels per se. In both groups, IUT treatment resulted in a significant decrease of the NT-proBNP concentration, whereas Hb and MCA-PSV measurements remained abnormal. By indicating the extent of cardiac stress NT-proBNP may be a useful marker in management of fetal anemia and IUT monitoring, especially in cases at risk for hydrops fetalis.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAuthor Contribution\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material, preparation, data collection and analysis were performed by P. Siebers and E. Weber, who have written the first draft of the manuscript. All authors commented on previous versions, read and approved the final manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eP Siebers: Data Collection, Manuscript writing\u003c/p\u003e\n\u003cp\u003eU Gembruch: Project development, Manuscript editing\u003c/p\u003e\n\u003cp\u003eWM Merz: Project development, Manuscript editing\u003c/p\u003e\n\u003cp\u003eF Recker: Data Collection, Manuscript editing\u003c/p\u003e\n\u003cp\u003eA M\u0026uuml;ller: Manuscript editing\u003c/p\u003e\n\u003cp\u003eB Strizek: Manuscript editing\u003c/p\u003e\n\u003cp\u003eA Geipel: Manuscript editing\u003c/p\u003e\n\u003cp\u003eC Berg: Manuscript editing\u003c/p\u003e\n\u003cp\u003eEC Weber: Data Collection, Project development, Manuscript writing\u003c/p\u003e\n\u003cp\u003eCompliance with Ethical Standards\u003c/p\u003e\n\u003cp\u003eFunding: The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eConflict of interest: The authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003eEthics approval: All procedures performed were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Approval was granted by the Ethics Committee of University of Bonn\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e(Study ID 208/08).\u003c/p\u003e\n\u003cp\u003eConsent to participate: Informed consent was obtained from all individual patients.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eNicolaides KH, Clewell WH, Mibashan RS, MEASUREMENT IN THE ASSESSMENT OF RED CELL ISOIMMUNISATION (1988) FETAL HAEMOGLOBIN. The Lancet 331:1073\u0026ndash;1075. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/S0140-6736(88)91896-X\u003c/span\u003e\u003cspan address=\"10.1016/S0140-6736(88)91896-X\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePrefumo F, Fichera A, Fratelli N, Sartori E (2019) Fetal anemia: Diagnosis and management. 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Exp Physiol 95:131\u0026ndash;139. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1113/expphysiol.2009.049379\u003c/span\u003e\u003cspan address=\"10.1113/expphysiol.2009.049379\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"archives-of-gynecology-and-obstetrics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"arch","sideBox":"Learn more about [Archives of Gynecology and Obstetrics](https://www.springer.com/journal/404)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/arch/default.aspx","title":"Archives of Gynecology and Obstetrics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"fetal anemia, hydrops fetalis, Parvovirus B19 infection, Rhesus incompatibility, intrauterine transfusion ","lastPublishedDoi":"10.21203/rs.3.rs-2347669/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2347669/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePurpose\u003c/p\u003e\n\u003cp\u003eIn adults and fetuses, N-terminal pro-B-type natriuretic peptide (NT-proBNP) is a marker of cardiac failure and myocardial remodelling. We examined the effect of anemia and intrauterine transfusion (IUT) on NT-proBNP concentrations in fetuses with anemia and established gestational age-dependent reference values of a control group.\u003c/p\u003e\n\u003cp\u003eMethods\u003c/p\u003e\n\u003cp\u003eWe analyzed NT-proBNP levels in anemic fetuses that underwent serial intrauterine transfusions (IUT), focusing on different causes and severity of anemia and comparing the results to a non-anemic control group.\u003c/p\u003e\n\u003cp\u003eResults\u003c/p\u003e\n\u003cp\u003eIn the control group, the average NT-proBNP concentration was 1339 ± 639 pg/ml, decreasing significantly with increasing gestational age (R=-74.04, T=-3.65, p=0.001). Subjects had significantly higher NT-proBNP concentrations before initiation of IUT therapy (p\u0026lt;0.001), showing fetuses with parvovirus B19 (PVB19) infection having the highest concentrations. Hydropic fetuses also showed an increased in NT-proBNP concentration compared to non-hydropic fetuses (p\u0026lt;0.001). During the course of therapy, NT-proBNP concentration before subsequent IUT decreased significantly from pathologically high levels, while MoM-Hb and MoM-MCA-PSV remained pathological.\u003c/p\u003e\n\u003cp\u003eConclusion\u003c/p\u003e\n\u003cp\u003eNT-pro BNP levels in healthy fetuses are higher than in postnatal life, decreasing with ongoing pregnancy. Anemia is a hyperdynamic state and its severity correlates with circulating NT-proBNP levels. Highest concentrations occur in fetuses with hydrops and with PVB19 infection, respectively. Treatment by IUT leads to a normalisation of NT-proBNP concentrations, so the measurement of its levels may be useful in therapy monitoring.\u003c/p\u003e","manuscriptTitle":"Fetal NT-proBNP levels and their course in severe anemia during intrauterine treatment","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-12-16 16:26:37","doi":"10.21203/rs.3.rs-2347669/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2023-01-09T08:09:33+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2022-12-14T11:03:47+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Archives of Gynecology and Obstetrics","date":"2022-12-12T20:18:21+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2022-12-12T16:35:34+00:00","index":"","fulltext":""},{"type":"submitted","content":"Archives of Gynecology and Obstetrics","date":"2022-12-10T17:33:50+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"archives-of-gynecology-and-obstetrics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"arch","sideBox":"Learn more about [Archives of Gynecology and Obstetrics](https://www.springer.com/journal/404)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/arch/default.aspx","title":"Archives of Gynecology and Obstetrics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"86b0b38e-fdfa-46e5-a024-12a9ed3f7355","owner":[],"postedDate":"December 16th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-10-16T20:15:09+00:00","versionOfRecord":{"articleIdentity":"rs-2347669","link":"https://doi.org/10.1007/s00404-023-07006-8","journal":{"identity":"archives-of-gynecology-and-obstetrics","isVorOnly":false,"title":"Archives of Gynecology and Obstetrics"},"publishedOn":"2023-03-26 20:08:00","publishedOnDateReadable":"March 26th, 2023"},"versionCreatedAt":"2022-12-16 16:26:37","video":"","vorDoi":"10.1007/s00404-023-07006-8","vorDoiUrl":"https://doi.org/10.1007/s00404-023-07006-8","workflowStages":[]},"version":"v1","identity":"rs-2347669","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2347669","identity":"rs-2347669","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}