Distribution of uterocervical angles of pregnant women at 16+0 to 23+6 weeks gestation with low risk for preterm delivery: First Vietnamese cohort of women with singleton pregnancies

Distribution of uterocervical angles of pregnant women at 16+0 to 23+6 weeks gestation with low risk for preterm delivery: First Vietnamese cohort of women with singleton pregnancies | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Distribution of uterocervical angles of pregnant women at 16+0 to 23+6 weeks gestation with low risk for preterm delivery: First Vietnamese cohort of women with singleton pregnancies Trang Nguyen Thi Hoang, Tam Vu Van, Huy Nguyen Vu Quoc This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2406007/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Apr, 2023 Read the published version in BMC Pregnancy and Childbirth → Version 1 posted 8 You are reading this latest preprint version Abstract Background: Cervical length (CL) measured by ultrasound in the second trimester is a predictor of spontaneous preterm birth (sPTB). The uterocervical angle (UCA) has recently been investigated as a parameter to identify women at risk of sPTB. This study aimed to investigate the UCAs’ distribution in singleton pregnant women at 16+0-23+6 weeks of gestation with low risk for sPTB. Methods: This was a prospective cohort study of 1,051 pregnant women with singleton pregnancies at low risk for preterm delivery. Pregnant women with a viable singleton fetus at 16+0-23+6 weeks of gestation were enrolled in the study conducted at the Haiphong Hospital of Obstetrics and Gynecology, Vietnam, from 09/2019 to 09/2020. CL and the UCA were assessed using transvaginal ultrasonography (TVS) by a single sonographer. Subjects were followed-up until the end of pregnancy, and maternal and neonatal outcomes were recorded. The UCAs’ range and their relationship with gestational age were evaluated using regression analysis. P<0.05 was considered statistically significant. Results: The normal range of the UCA (5th-95th percentiles) was 46.47° (95% CI, 40.27°-51.81°) to 127.06° (95% CI, 123.02°-130.71°). The UCAs in the preterm birth (<37 weeks) and full-term groups were 117.86°±20.25° and 83.80°±24.18°, respectively (p<0.001). Linear regression analysis showed a significant change in the UCA range from 16+0 to 23+6 weeks of gestation (2.51 degrees per week, p<0.001). The quadratic function yielded the highest correlation coefficient in the variation rule of the UCA values (r2=0.051). A total of 42/63 (66.7%) patients with preterm birth <37 weeks had a UCA above the 75th percentile. The rate of UCA values ≥95° was significantly higher in the sPTB group than in full-term delivery group (88.9% vs. 31.3%, p<0.001). Conclusions: The UCA values in the preterm birth <37 weeks group were significantly wider in the full-term delivery group (p<0.001), and the majority of women with preterm birth had an UCA ≥ 95° compared with those with full-term delivery (p<0.001). It is advisable to monitor the UCA, especially in pregnant women with a UCA value ≥ 95° at 16+0-23+6 weeks of gestation. uterocervical angle (UCA) singleton pregnancy preterm birth Figures Figure 1 Figure 2 Figure 3 Figure 4 Background According to the World Health Organization, a preterm birth (PTB) is defined as a live birth occurring between 20 + 0 and 36 + 6 gestational weeks [ 1 ]. Globally, the prematurity rate is 10.6%, resulting in nearly one million neonatal deaths each year [ 2 , 3 ]. In Vietnam in 2014, the data showed a PTB rate of 9%, ranking Vietnam 21st in the world [ 4 ]. Preterm birth is a major cause of neonatal morbidity and mortality, mostly due to immature respiratory organs, cerebral hemorrhage and infection, which can lead to long-term neurological deficits such as intellectual impairment, cerebral palsy, chronic lung disease, deafness and blindness [ 3 , 5 ]. Approximately one-third of all preterm births are medically indicated, and the rest occur spontaneously, which remains a challenge in obstetric care [ 6 ]. Early identification of subjects at risk of spontaneous preterm birth (sPTB) from the general pregnant population is essential for offering adequate prevention measures. Many strategies have been developed to predict and prevent spontaneous prematurity. Until now, a previous history of sPTB and a short cervix were the main screening criteria [ 7 , 8 ]. Sonographic cervical length measurement has been consistently shown to be an efficient and cost-effective strategy in the prediction of sPTB in asymptomatic singleton pregnant women [ 9 – 11 ]. A CL cutoff ≤ 25 mm by transvaginal ultrasound is considered a strong risk predictor of preterm birth in singleton pregnant women. However, its detection rate for spontaneous preterm deliveries at < 34 weeks is only approximately 55%, with a 10% false-positive rate [ 12 , 13 ]. Therefore, additional screening parameters are needed to identify pregnant women at risk of preterm birth to provide timely preventive measures. The uterocervical angle (UCA) has recently been studied as a parameter to identify women at risk for sPTB [ 14 ]. If the UCA is more obtuse, the gravity of the uterus and the fetus acting on the internal os tends to be along the direction of the cervix, which can lead to shortening of the cervix, and this is one of the factors causing preterm birth [ 15 , 16 ]. UCA measurement, performed by transvaginal ultrasonography (TVS) during the second trimester of gestation, has been reported as a high-performance screening tool in predicting preterm birth [ 17 , 18 ]. Studies by Dziadosz et al. [ 18 ] and Knight et al. [ 19 ] found that the combination of UCA with cervical length measurements provides a stronger predictor of preterm birth. A recent study by Luechathananon et al. [ 20 ], the first prospective observational cohort study of its kind, showed that in subjects with threatened preterm labor and a mean gestational age of 35 + 0 (range, 33 + 0 , 36 + 0 ) weeks, UCA measurement by using TVS can be considered a useful tool for predicting preterm birth. Moreover, there is still a lack of in-depth studies evaluating the real-life distribution of UCA values in pregnant women with term or preterm deliveries, and there is still no consensus on the appropriate gestational age during the second trimester at which to perform UCA measurement to identify women at risk of preterm birth. This study aimed to investigate the distribution of UCA values in singleton pregnant women at 16 + 0 − 23 + 6 weeks gestation from a cohort consisting of women with term and preterm deliveries. Methods Study design This study was a longitudinal cohort study conducted from September 2019 to September 2020 at the Department of Pregnancy Management and Prenatal Diagnosis of Haiphong Hospital of Obstetrics and Gynecology, Vietnam. Sample size calculation The sample size of this study was estimated using the following formula: L: number of gestational age groups; there were 8 groups from 16 + 0 to 23 + 6 weeks of gestation. Z (1−α/2) = 1.96, δ value = 0.025, x̅ : mean of UCA, S : standard deviation. According to Dagdeviren et al. [ 21 ], x̅ = 110.57 mm and S = 13.46 mm. Based on these values, the minimum sample size was 729 subjects. Study population All singleton pregnant women aged 18 to 40 years old and between 16 + 0 and 23 + 6 weeks of gestation with viable fetuses who were examined and managed at the Department of Pregnancy Management & Prenatal Diagnosis of Haiphong Hospital of Obstetrics and Gynecology between September 2019 and September 2020 were included in the study. The exclusion criteria were as follows: 1) a history of sPTB or second trimester miscarriage (miscarriage at 13 + 0 -19 + 6 weeks gestation) [ 22 ], 2) a short CL (CL ≤ 25 mm), 3) signs of threatened miscarriage or preterm birth, 4) severe fetal malformations, 5) medically indicated preterm birth, 6) a cervical mass or previous cervical surgery, 7) the use of available preterm birth prevention methods (micronized progesterone, cerclage, cervical pessary), and 8) loss of follow-up. A total of 1,165 pregnant women with singleton pregnancies at 16 + 0 to 23 + 6 weeks gestation were voluntary participants in this study and were recruited according to the recruitment guidelines. Each participant underwent TVS once for CL and UCA measurements and was followed-up until delivery. Women who delivered at other hospitals were contacted via telephone. After excluding 114 participants at high risk for sPTB or loss of follow-up, 1,051 pregnant women were included in the final analysis (Fig. 1 ). Assessment of cervical length and the uterocervical angle The cervical length and uterocervical angle measurements were performed by a single sonographer who was certified and monitored by the Maternal Fetal Medicine Foundation. The ultrasound machines used for measurements were the Samsung Medison WS80A (Korea) and GE Voluson E6 (GE Healthcare Korea) with a transvaginal probe (frequency 4.0–9.0 MHz). Patients had an empty bladder, and excessive pressure on the cervix was avoided. The CL measurements were performed following the standard method of The Fetal Medicine Foundation, tracing a single straight line from the internal to external os. Because the guidelines for UCA are not yet established, the UCA was measured following previously published protocols, according to the method described by Dziadosz et al. [ 18 ]. In short, a first line is placed from the internal os to the external os irrespective of whether the cervix is straight or curved. A second line is then drawn to delineate the lower uterine segment. This ray is traced up the anterior uterine segment to a distance allowed by the preloaded image. Ideally, the second ray reaches 3 cm up the lower uterine segment to establish an adequate measurement. The angle between the two lines is the UCA value (Fig. 2 ). Each participant had three images measured to reduce measurement bias, and the most obtuse UCA from the three images was used. The patients’ demographic characteristics, ultrasound images, expected date of delivery, obstetric complications and perinatal outcome data were recorded. Outcome measures The mean difference in the uterocervical angles among pregnant women with term and preterm deliveries (before 37 weeks of gestation) was defined as the primary outcome parameter. The secondary outcome was the percentage of preterm birth women before 37 weeks that had UCA values lying on the 75th percentile curve. Statistical analysis All analyses were performed using SPSS version 26.0 (SPSS, Inc., Chicago, IL). Student’s t test was used to evaluate the difference between two means, and p < 0.05 was considered statistically significant. Calculating the correlation between two quantities according to each function y = f(x) (y is anthropometric quantities, x is gestational age), there was a correlation when r > 0.5. The distribution of UCA values was visualized using a scatter plot against gestational age. Predicted median and 5th and 95th percentiles of UCA values with 95% confidence intervals according to GA were estimated using quantile regression, which allows the possibility to detect whether the range of UCA values changes with GA, as well as the display of the confidence band around each percentile. Kurtosis and skewness calculations were performed to determine the distribution of cervical angle measurements according to gestational age. If there was a normal distribution, the values corresponding to the 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles were measured by the following formulas: + 25th, 75th percentile = x̅ ± 1.88. SD + 5th, 95th percentile = x̅ ± 1.645. SD + 10th, 90th percentile = x̅ ± 1.28. SD + The 50th percentile = x̅ = the result from solving a corresponding equation (with the highest r) and the corresponding values [ 23 , 24 ]. The mean values were determined after solving the selective equation (with the highest r), and the values corresponding to the percentiles calculated according to the above formula were the basis for establishing the UCA percentile chart according to gestational age. The research proposal was approved by the Ethical Council in Biomedical Research of Hue University of Medicine and Pharmacy, Vietnam (Ethics Committee ID number H2020/035) and the Scientific Council of Haiphong Hospital of Obstetrics and Gynecology, Vietnam (IEC, 1186/QD-BVPSHP). All participants voluntarily signed a written informed consent form after hearing a full explanation of the purpose of this study. Results A total of 1,165 pregnant women were included in this cohort. During the follow-up period, 114 women at high risk for sPTB or loss to follow-up were identified and excluded from the final analysis. The exclusion criteria were as follows: short cervical length (22 women), history of sPTB (18 women), complete placental previa (5 women), placental abruption (2 women), severe preeclampsia (4 women), hydrops fetalis (2 women), severe fetal malformations (5 women), fetal chromosomal abnormality (2 with trisomy 21), fetal intrauterine growth restriction (5 women), serious thalassemia fetal (1 woman), fetal distress (4 women), amniotic fluid infection (1 woman), previous cervical surgery (2 women), the use of available preterm birth prevention methods (micronized progesterone, cerclage, cervical pessary) (20 women), and loss to follow-up (21 women). Overall, 1,051 pregnant women who met the study criteria were divided into two groups: a full-term delivery group (≥ 37 weeks, 988 women) and a preterm delivery group (before 37 weeks, 63 women). A full comparison of the demographic and clinical data of the two groups is presented in Table 1 . The mean UCA value increased with GA from 16 + 0 to 23 + 6 weeks (Table 2 ), and the difference was statistically significant (p < 0.001). Table 1 Study subjects’ characteristics. Characteristics Full-term delivery (≥ 37 weeks) (n = 988) Preterm birth < 37 weeks (n = 63) P value Maternal characteristics Age (years) 28.83 ± 5.06 29.19 ± 5.02 0.5913 BMI (kg/m 2 ) 20.53 ± 2.51 20.37 ± 2.07 0.676 Parity 1.2 ± 0.5 1.3 ± 0.7 0.2685 Gestational age at TVS (weeks) 19.74 ± 2.31 20.90 ± 1.79 < 0.001 CL (mm) 36.52 ± 5.07 32.05 ± 4.37 < 0.001 UCA (degrees) 83.80 ± 24.18 117.86 ± 20.25 < 0.001 UCA ≥ 95 o 309 (31.3%) 56 (88.9%) < 0.001 Neonatal characteristics and outcomes Gestational age at birth (weeks) 38.41 ± 0.90 34.36 ± 2.01 < 0.001 Birthweight (gram) 3182.79 ± 285.42 2412.69 ± 480.42 < 0.001 C-section 410 (41.5%) 8 (12.7) < 0.001 NICU admission 34 (3.44) 33(54.10) < 0.001 Deaths 0 2 - Table 2 Mean value of the UCA at 16 + 0 to 23 + 6 weeks gestation. GA N Mean SD 16 + 0 − 1 6 + 6 17 + 0 − 1 7 + 6 18 + 0 − 1 8 + 6 19 + 0 − 1 9 + 6 20 + 0 − 2 0 + 6 21 + 0 − 2 1 + 6 22 + 0 − 2 2 + 6 23 + 0 − 2 3 + 6 112 110 149 82 110 145 215 128 74.65 79.15 81.07 88.30 86.96 90.71 89.82 92.21 22.19 24.76 27.32 20.05 24.15 23.22 26.93 24.32 p < 0.001 In the preterm birth group, the mean CL was significantly shorter (36.52 ± 5.07 mm vs. 32.05 ± 4.37 mm, p < 0.001), and the mean UCA value was significantly wider than those in the full-term group (83.80 ± 24.18° vs. 117.86 ± 20.25°) (p 0.05). To determine the distribution characteristics of observed values in each gestational age subgroup, we calculated the Kurtosis coefficient and skewness coefficient, which proves that the distribution is normal when the Kurtosis coefficient ≤ ± 2 and skewness coefficient ≤ ± 2. These distribution characteristics were determined to calculate the values corresponding to the percentile curve. If the distribution was normal, the percentile curve was measured by the following formula: percentile curve = x̅ ± k.SD. The results of the Kurtosis coefficient and skewness coefficient of the UCA value according to GA subgroups are described in Table 3 . Table 3 Kurtosis coefficient and skewness coefficient of the UCA at 16 + 0 to 23 + 6 weeks gestation. GA Kurtosis coefficient Skewness coefficient 16 + 0 − 1 6 + 6 17 + 0 − 1 7 + 6 18 + 0 − 1 8 + 6 19 + 0 − 1 9 + 6 20 + 0 − 2 0 + 6 21 + 0 − 2 1 + 6 22 + 0 − 2 2 + 6 23 + 0 − 2 3 + 6 0.247 0.550 0.092 0.430 0.345 0.119 0.322 0.071 0.281 1.193 0.318 0.783 0.168 -0.149 1.384 0.095 To demonstrate and determine the rule of the UCA measurement variation with a GA from 16 + 0 to 23 + 6 weeks, we determined the relationship between the UCA value (y) and GA (x) according to a linear function, a quadratic function and a cubic function. The function with the highest correlation coefficient correctly represented the variation rule of UCA values, which was the cubic function (with r 2 = 0.051). The line representing the UCA variation rule connects the mean values after solving the cubic function, y = -81.11x + 13.65x – 0.27x 2 (Fig. 3 ). Based on the above function representing the selected variation rule, Table 4 presents the mean values and corresponding values for the 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentile curves. Table 4 GA-based UCAs corresponding to the 5th, 10th, 25th, 50th, 75th, 90th, and 95th . GA N SD Distribution of UCA values according to percentile 5% 10% 25% 50% 75% 90% 95% 16 + 0 − 1 6 + 6 112 22.19 39.82 48.11 59.32 73.55 88.62 104.64 114.10 17 + 0 − 1 7 + 6 110 24.76 45.13 50.73 61.14 79.59 91.79 105.94 127.75 18 + 0 − 1 8 + 6 149 27.32 30.03 45.32 64.80 79.86 100.39 114.50 124.44 19 + 0 − 1 9 + 6 82 20.05 58.23 66.28 73.17 85.60 101.31 113.52 125.20 20 + 0 − 2 0 + 6 110 24.15 48.72 56.00 70.90 85.68 102.07 119.73 132.69 21 + 0 − 2 1 + 6 145 23.22 52.53 59.58 74.90 87.93 106.28 119.33 131.28 22 + 0 − 2 2 + 6 215 26.93 44.30 57.84 72.44 90.37 105.14 122.35 128.48 23 + 0 − 2 3 + 6 128 24.32 53.00 60.84 75.24 91.20 109.58 122.83 132.56 Linear regression analysis showed a significant change in the range of UCA values from 16 + 0 to 23 + 6 weeks of gestation (increase of 2.51 degrees per week, p < 0.001, Fig. 3 ). The range of the UCA at the 5th to 95th percentile ranges from 38.96° (95% CI, 35.45°- 44.31°) to 133.70° (95% CI, 128.92°- 139.32°). There were 42/63 women with preterm birth before 37 weeks with a UCA value above the 90th percentile and 53/53 women with preterm birth before 37 weeks with a UCA value ≥ 95°, accounting for 66.7% and 84.1%, respectively (Fig. 4 ). Discussion Our study of 1,051 singleton pregnant women at 16 + 0 to 23 + 6 weeks gestation with low risk for sPTB who were treated at Haiphong Hospital of Obstetrics and Gynecology from September 2019 to September 2020 showed that the normal range of UCA values at the 5th to 95th percentile was from 46.47° (95% CI, 40.27° − 51.81°) to 127.06° (95% CI, 123.02° − 130.71°) (Fig. 4 ), with significant changes during this GA period (increase of 2.51 degrees per week, p < 0.001, Fig. 3 ). Similarly, the study of Llobet et al. [ 25 ] with 275 singleton pregnant women showed that the mean UCA values increased from the first to the second trimester with statistical significance (84.2° versus 94.5°, p = 0.019). Sawaddisan et al. [ 26 ] (Thailand, 2020) studied 372 singleton pregnant women at GAs from 16 + 0 to 23 + 6 weeks and showed that UCA values changed according to GA, but this change was not statistically significant (increase of 0.3° per week, p = 0.757). As shown in Table 1 , the mean values of the UCA in the preterm birth before 37 weeks group were significantly wider than those in the full-term delivery group (83.80° ± 24.18° vs. 117.86° ± 20.25°, p < 0.001). Sochacki-Wojcicka et al. [ 27 ] also found that there was a statistically significant difference in the mean UCA value between the preterm birth group and the full-term delivery group in the first trimester (115.5° vs. 85°, p = 0.0002) and 2nd trimester (126° vs. 91.5°, p < 0.0001). The study of Llobet et al. [ 25 ] with the aim of determining the correlation of the cervical angle with preterm birth also concluded that the UCA in the second trimester in the preterm birth group was wider than that in the full-term delivery group [(105.16° vs. 94.53°, p = 0.015, RR = 0.821 (95% CI, 0.74–0.97)]. Table 1 also demonstrates that the rate of preterm birth before 37 weeks in our study was 6% (63/1051 women). The majority of women with preterm birth had a UCA ≥ 95° compared with those with full-term delivery (88.9% vs. 31.3%, p < 0.001). Recently, several studies have shown that the UCA can be useful in predicting sPTB [ 18 , 25 , 27 – 29 ]. Dziadosz et al. [ 18 , 30 ] observed that second trimester UCA measurement could detect the possibility of preterm birth at < 37 weeks with a sensitivity of 80% when the angle was ≥ 95° and at < 34 weeks with a sensitivity of 81% when the UCA was ≥ 105°. The same authors also reported that when they performed stepwise linear regression analysis, the UCA was dependent on maternal age, obesity at conception, nulliparity, and race. Lynch et al. [ 31 ] also found that a UCA ≥ 105° at 19 to 25 weeks gestation was associated with the risk of preterm birth before 37 weeks; however, only pregnant women with a short cervix ≤ 25 mm were included in this study. A recent study by Singh et al. [ 28 ] also revealed that the risk of spontaneous preterm delivery was higher in women with obtuse UCAs (≥ 95 degrees), with a sensitivity of 86.7%, specificity of 93.0%, positive predictive value of 83.0%, and negative predictive value of 94.6%. It can be explained that if the UCA is obtuse, the gravity of the uterus and the fetus acting on the internal os tend to be along the direction of the cervix, which can lead to shortening of the cervix, and this is one of the factors causing preterm birth. Therefore, the function of cervical cerclage based on this mechanism is not only to support the cervix to evenly distribute the force from the uterus but also to change the UCA from obtuse to acute, changing the force of the uterus to the posterior fornix to avoid shortening the cervix. This has been proven through the study of Cannie et al. [ 15 ]. They analyzed CL and UCA measurements in 2 groups of pregnant women: 198 women with no high risk of preterm birth and 73 women with a high risk of preterm birth who had an Arabin pessary at 14 to 33 weeks gestation. The authors performed cervical magnetic resonance imaging before inserting the Arabin pessary and monthly follow-up until the pessary was removed. The results showed that in the group of pregnant women with a low risk of PTB, the UCA measurement did not change, but the CL values decreased significantly with GA (r = − 0.15, p < 0.05). In the high-risk preterm birth group, 63 patients who delivered after 34 weeks had a mean UCA value that was significantly reduced compared to that before the Arabin pessary was inserted (132° vs. 146°, p 0.05). To demonstrate the clinical applicability of the established UCA percentile chart, we performed the distribution of UCA in the PTB before 37 weeks gestation group on the percentile chart of the singleton pregnant woman at 16 + 0 to 23 + 6 weeks gestation (Fig. 4 ), and we found that most of the women with preterm birth before 37 weeks had a UCA value above the 75th percentile (42/63 women, accounting for 66.7%). Based on the results of this study, we have the same opinion as some authors that the UCA values in women with PTB is wider than that in women with term delivery. Preterm birth rates are increased in women with obtuse uterocervical angles. Thus, should we consider the 75th percentile on the above UCA percentile chart as a limit to predict PTB before 37 weeks in pregnant women at low risk for preterm delivery? More in-depth studies with a large sample size are necessary to prove the prognostic value of UCA measurements in the prediction of preterm birth, especially in combination with a short cervical length. In clinical practice, measuring the CL by TVS at 16–24 weeks gestation is the current recommended screening method for preterm birth (SMFM, ACOG, ISUOG) [ 32 – 34 ]. Measuring the UCA and CL (16–24 weeks) by vaginal ultrasound at the same time can increase the efficiency of preterm birth screening; additionally, it is convenient and saves money to measure both of these parameters at the same time in pregnancy. This study had three major strengths. First, this is the first study in Vietnam to establish the percentile chart of UCA measurements in singleton pregnant women at 16 + 0 to 23 + 6 weeks gestation with low risk for sPTB. Second, the measurement of all uterocervical angles was performed by a single obstetrician to control for interobserver variability, and the prospective nature of the study to control for the risk of information bias, focusing on investigating the UCA values of a large study sample, can also be considered strengths of the study. Third, the study subjects included only pregnant women at low risk for sPTB (without a history of sPTB or short cervical length), which could have eliminated the role and impact of these factors on pregnancy outcomes. However, the present study had several limitations. First, women with several maternal conditions that predispose women to sPTB, such as a history of sPTB, short cervical length, and previous cervical surgery, were excluded from the study sample, limiting the representativeness of the general population of pregnant women. Second, selecting pregnant women from a single center can affect the generalizability of our findings. Conclusions Our findings provided baseline information about the normal range of UCA values in singleton pregnant women at 6 + 0 to 23 + 6 weeks with low risk for sPTB. The range of UCA values at the 5th to 95th percentile ranged from 46.47 degrees (95% CI, 40.27° − 51.81°) to 127.06 degrees (95% CI, 123.02° − 130.71°). There was a significant change in the range of UCA values from 16 + 0 to 23 + 6 weeks gestation in singleton pregnant women at low risk for sPTB (increase of 2.51 degrees per week, p < 0.001). The values of the UCA in the preterm birth before 37 weeks group was significantly wider than that in the full-term delivery group (117.86° ± 20.25° vs. 83.80° ± 24.18°, p < 0.001) and the majority of women with preterm birth had a UCA value ≥ 95° compared with those with full-term delivery (88.9% vs. 31.3%, p < 0.001). Most of the women with preterm birth before 37 weeks had a UCA value ≥ 95° (53/63 women, accounting for 84.1%) and above the 75th percentile (42/63 women, accounting for 66.7%). Therefore, it is advisable to monitor the UCA, especially in pregnant women with a UCA value ≥ 95° at 16 + 0 to 23 + 6 weeks of gestation. Abbreviations CL: Cervical length UCA: Uterocervical angle TVS: Transvaginal ultrasonography PTB: Preterm birth sPTB: Spontaneous preterm birth GA: Gestational age Declarations Ethics approval and consent to participate The research proposal was approved by the Ethical Council in Biomedical Research of Hue University of Medicine and Pharmacy, Vietnam (Ethics Committee ID number H2020/035) and the Scientific Council of Haiphong Hospital of Obstetrics and Gynecology, Vietnam (IEC, 1186/QD-BVPSHP). All participants voluntarily signed a written informed consent form after hearing a full explanation of the purpose of this study. Consent for publication Not applicable. Availability of data and materials The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request. Competing interests The authors declare that they have no competing interests. Funding This research did not receive specific grants from funding agencies in the public, commercial or nonprofit sectors. Authors' contributions N.T.H.T., V.V.T. and N.V.Q.H. designed the study. N.T.H.T. and V.V.T. performed data collection. N.T.H.T. and N.V.Q.H. performed statistical analyses and wrote the first manuscript. N.T.H.T., V.V.T. and N.V.Q.H. critically revised successive drafts of the paper. All authors read and approved the final manuscript. Acknowledgements The authors would like to thank all the pregnant women who agreed to participate in this study. References De Costa A, Moller AB, Blencowe H, Johansson EW, Hussain-Alkhateeb L, Ohuma EO, et al. Study protocol for WHO and UNICEF estimates of global, regional, and national preterm birth rates for 2010 to 2019. PLoS ONE. 2021;16:e0258751. Chawanpaiboon S, Vogel JP, Moller AB, Lumbiganon P, Petzold M, Hogan D, et al. 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Ultrasound Obstet Gynecol. 2013;42:426–33. Arabin B, Alfirevic Z. Cervical pessaries for prevention of spontaneous preterm birth: past, present and future. Ultrasound Obstet Gynecol. 2013;42:390–9. Daskalakis G, Theodora M, Antsaklis P, Sindos M, Grigoriadis T, Antsaklis A, et al. Assessment of uterocervical angle width as a predictive factor of preterm birth: a systematic review of the literature. Biomed Res Int. 2018;2018:1837478. Dziadosz M, Bennett TA, Dolin C, Honart AW, Pham A, Lee SS, et al. Uterocervical angle: a novel ultrasound screening tool to predict spontaneous preterm birth. Am J Obstet Gynecol. 2016;215:376.e1-7. Knight JC, Tenbrink E, Onslow M, Patil AS. Uterocervical angle measurement improves prediction of preterm birth in twin gestation. Am J Perinatol. 2018;35:648–54. Luechathananon S, Songthamwat M, Chaiyarach S. Uterocervical angle and cervical length as a tool to predict preterm birth in threatened preterm labor. Int J Womens Health. 2021;13:153–9. Dagdeviren E, Çetin BA, Mathyk BA, Koroglu N, Topcu EG, Yuksel MA. Can uterocervical angles successfully predict induction of labor in nulliparous women? Eur J Obstet Gynecol Reprod Biol. 2018;228:87–91. American College of Obstetricians and Gynecologists' Committee on Practice Bulletins—Obstetrics. Second-Trimester Abortion: ACOG practice bulletin, number 135. Obstet Gynecol. 2013;121(6):1394–406. National Center for Health Statistics. National health and nutrition examination survey centers for disease control and prevention growth charts. US Department of Health and Human Services: United States; 2008. Duyet PT. Clinical and ultrasound diagnosis in obsetrics and gynecology. Hanoi: Medical Publishing House; 2013. Llobet AF, Martí LR, Higueras T, Fernández IZC, Portalés AG, Canino MMG, et al. The uterocervical angle and its relationship with preterm birth. J Matern Fetal Neonatal Med. 2018;31:1881–4. Sawaddisan R, Kor-Anantakul O, Pruksanusak N, Geater A. Distribution of uterocervical angles in the second trimester of pregnant women at low risk for preterm delivery. J Obstet Gynaecol. 2021;41:77–82. Sochacki-Wójcicka N, Wojcicki J, Bomba-Opon D, Wielgos M. Anterior cervical angle as a new biophysical ultrasound marker for prediction of spontaneous preterm birth. Ultrasound Obstet Gynecol. 2015;46:377–8. Singh PK, Srivastava R, Kumar I, Rai S, Pandey S, Shukla RC, et al. Evaluation of uterocervical angle and cervical length as predictors of spontaneous preterm birth. Indian J Radiol Imaging. 2022;32:10–5. Niyomyam P, Charoenvidhya D, Uerpairojkit B. Uterocervical angle measurement for prediction spontaneous preterm birth in twin pregnancy. Thai J Obstet Gynaecol. 2020;30:362–8. Sur B, Misra S, Dash S. Evaluation of the anterior cervical angle of the uterus to predict spontaneous preterm birth. Int J Reprod Contracept Obstet Gynecol. 2017;6:2323–7. Lynch TA, Szlachetka K, Seligman NS. Ultrasonographic change in uterocervical angle is not a risk factor for preterm birth in women with a short cervix. Am J Perinatol. 2017;34:1058–64. Berghella V, Palacio M, Ness A, Alfirevic Z, Nicolaides KH, Saccone G. Cervical length screening for prevention of preterm birth in singleton pregnancy with threatened preterm labor: systematic review and meta-analysis of randomized controlled trials using individual patient-level data. Ultrasound Obstet Gynecol. 2017;49:322–9. Coutinho CM, Sotiriadis A, Odibo A, Khalil A, D'Antonio F, Feltovich H, et al. ISUOG practice guidelines: role of ultrasound in the prediction of spontaneous preterm birth. Ultrasound Obstet Gynecol. 2022;60:435–56. American College of Obstetricians and Gynecologists' Committee on Practice Bulletins—Obstetrics. Prediction and prevention of spontaneous preterm birth: ACOG practice bulletin, number 234. Obstet Gynecol. 2021;138:e65–90. Additional Declarations No competing interests reported. Supplementary Files UterocervicalangleTrangNTHTamVVHuyNVQ.sav Cite Share Download PDF Status: Published Journal Publication published 28 Apr, 2023 Read the published version in BMC Pregnancy and Childbirth → Version 1 posted Editorial decision: Major revision 31 Jan, 2023 Reviews received at journal 21 Jan, 2023 Reviewers agreed at journal 09 Jan, 2023 Reviewers invited by journal 09 Jan, 2023 Editor assigned by journal 03 Jan, 2023 Editor invited by journal 30 Dec, 2022 Submission checks completed at journal 30 Dec, 2022 First submitted to journal 22 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies 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-2406007","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":163921778,"identity":"ae991cde-fc7f-4890-a672-59cce63bf53e","order_by":0,"name":"Trang Nguyen Thi Hoang","email":"","orcid":"","institution":"Hue University of Medicine and Pharmacy, Hue University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Trang","middleName":"Nguyen Thi","lastName":"Hoang","suffix":""},{"id":163921779,"identity":"46765ea9-f6a4-4d62-b3e1-654a6a72bd09","order_by":1,"name":"Tam Vu Van","email":"","orcid":"","institution":"Hai phong University Of Medicine and Pharmacy","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Tam","middleName":"Vu","lastName":"Van","suffix":""},{"id":163921780,"identity":"dbbc2d00-50b0-4380-9509-5738de0d0305","order_by":2,"name":"Huy Nguyen Vu Quoc","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/UlEQVRIiWNgGAWjYHACNiC2SQAzeaBcMIOAljTStRxGaEFlYAHmEsnbHvO2nc8zON6d+OANw+E8PokExgdv2xgSt+PQYjkjrdyYt+12scGZs5sN5zAcLmaTSGA2nAvUsrMBuxaDM2fMpIFaEjfcyN0mzfvvcGIbzwE2oAiDscEBvFrOJW64/3b7bx4GsBb233i1HO8BaTkAtIV3GzNYC3sDGzNQixxuLW1lknPOJSfOPJO7WXIOQzpQS2MzUEQCt5bDzNsk3pTZJfYdP7vxwxsG68T5zcwHP7wps+HBpQWki4GRDUWAsQFISOBUD9bC8Aef/CgYBaNgFIx4AAASGVuBT4SqsgAAAABJRU5ErkJggg==","orcid":"","institution":"Hue University of Medicine and Pharmacy, Hue University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Huy","middleName":"Nguyen Vu","lastName":"Quoc","suffix":""}],"badges":[],"createdAt":"2022-12-22 16:29:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2406007/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2406007/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s12884-023-05597-3","type":"published","date":"2023-04-28T20:35:31+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":31126384,"identity":"a20084e7-e5c9-4386-9340-1fe7ddbc4c80","added_by":"auto","created_at":"2023-01-04 22:15:04","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":469689,"visible":true,"origin":"","legend":"\u003cp\u003eStudy diagram.\u003c/p\u003e","description":"","filename":"Fig1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2406007/v1/a6f0ad832a5672bdd3950ee4.jpg"},{"id":31125548,"identity":"f9a45195-c6e4-45e0-927a-aa810835910f","added_by":"auto","created_at":"2023-01-04 22:07:04","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":318940,"visible":true,"origin":"","legend":"\u003cp\u003eTransvaginal ultrasound measurement of the UCA. Measurement of the triangular segment between the lower uterine segment and the cervical canal.\u003c/p\u003e","description":"","filename":"Fig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2406007/v1/8ca9809352f9e11e1d8da497.jpg"},{"id":31125552,"identity":"5e43389b-43b5-4295-a1de-316322e95ec2","added_by":"auto","created_at":"2023-01-04 22:07:04","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":334518,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of UCA values according to gestational age.\u003c/p\u003e","description":"","filename":"Fig3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2406007/v1/0f55c29cf5657cafbf5e11ff.jpg"},{"id":31125553,"identity":"939ac240-ac42-4c07-a247-b21c810e531e","added_by":"auto","created_at":"2023-01-04 22:07:04","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":226649,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of UCA values in the preterm birth \u0026lt;37 weeks group.\u003c/p\u003e","description":"","filename":"Fig4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2406007/v1/2e0ca0f294d959e70e8a309a.jpg"},{"id":44728090,"identity":"ea5c9fe5-8f93-49aa-ba1a-fca2aac5c5f6","added_by":"auto","created_at":"2023-10-16 20:58:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":728247,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2406007/v1/e5fe7dc4-8428-46d1-b900-75e4bbf3aed3.pdf"},{"id":31125550,"identity":"331f3cd3-4627-4b67-a34f-6a2d6bbaa016","added_by":"auto","created_at":"2023-01-04 22:07:04","extension":"sav","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":69230,"visible":true,"origin":"","legend":"","description":"","filename":"UterocervicalangleTrangNTHTamVVHuyNVQ.sav","url":"https://assets-eu.researchsquare.com/files/rs-2406007/v1/24bffd3e2f8cd589ff471266.sav"}],"financialInterests":"No competing interests reported.","formattedTitle":"Distribution of uterocervical angles of pregnant women at 16+0 to 23+6 weeks gestation with low risk for preterm delivery: First Vietnamese cohort of women with singleton pregnancies","fulltext":[{"header":"Background","content":"\u003cp\u003eAccording to the World Health Organization, a preterm birth (PTB) is defined as a live birth occurring between 20\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e and 36\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Globally, the prematurity rate is 10.6%, resulting in nearly one million neonatal deaths each year [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In Vietnam in 2014, the data showed a PTB rate of 9%, ranking Vietnam 21st in the world [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Preterm birth is a major cause of neonatal morbidity and mortality, mostly due to immature respiratory organs, cerebral hemorrhage and infection, which can lead to long-term neurological deficits such as intellectual impairment, cerebral palsy, chronic lung disease, deafness and blindness [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Approximately one-third of all preterm births are medically indicated, and the rest occur spontaneously, which remains a challenge in obstetric care [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Early identification of subjects at risk of spontaneous preterm birth (sPTB) from the general pregnant population is essential for offering adequate prevention measures. Many strategies have been developed to predict and prevent spontaneous prematurity. Until now, a previous history of sPTB and a short cervix were the main screening criteria [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Sonographic cervical length measurement has been consistently shown to be an efficient and cost-effective strategy in the prediction of sPTB in asymptomatic singleton pregnant women [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. A CL cutoff\u0026thinsp;\u0026le;\u0026thinsp;25 mm by transvaginal ultrasound is considered a strong risk predictor of preterm birth in singleton pregnant women. However, its detection rate for spontaneous preterm deliveries at \u0026lt;\u0026thinsp;34 weeks is only approximately 55%, with a 10% false-positive rate [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Therefore, additional screening parameters are needed to identify pregnant women at risk of preterm birth to provide timely preventive measures.\u003c/p\u003e \u003cp\u003eThe uterocervical angle (UCA) has recently been studied as a parameter to identify women at risk for sPTB [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. If the UCA is more obtuse, the gravity of the uterus and the fetus acting on the internal os tends to be along the direction of the cervix, which can lead to shortening of the cervix, and this is one of the factors causing preterm birth [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. UCA measurement, performed by transvaginal ultrasonography (TVS) during the second trimester of gestation, has been reported as a high-performance screening tool in predicting preterm birth [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Studies by Dziadosz et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] and Knight et al. [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] found that the combination of UCA with cervical length measurements provides a stronger predictor of preterm birth. A recent study by Luechathananon et al. [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], the first prospective observational cohort study of its kind, showed that in subjects with threatened preterm labor and a mean gestational age of 35\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e (range, 33\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e, 36\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e) weeks, UCA measurement by using TVS can be considered a useful tool for predicting preterm birth. Moreover, there is still a lack of in-depth studies evaluating the real-life distribution of UCA values in pregnant women with term or preterm deliveries, and there is still no consensus on the appropriate gestational age during the second trimester at which to perform UCA measurement to identify women at risk of preterm birth. This study aimed to investigate the distribution of UCA values in singleton pregnant women at 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u0026minus;\u0026thinsp;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation from a cohort consisting of women with term and preterm deliveries.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv class=\"Section2\" id=\"Sec3\"\u003e\n \u003ch2\u003eStudy design\u003c/h2\u003e\n \u003cp\u003eThis study was a longitudinal cohort study conducted from September 2019 to September 2020 at the Department of Pregnancy Management and Prenatal Diagnosis of Haiphong Hospital of Obstetrics and Gynecology, Vietnam.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec4\"\u003e\n \u003ch2\u003eSample size calculation\u003c/h2\u003e\n \u003cp\u003eThe sample size of this study was estimated using the following formula:\u003c/p\u003e\n \u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n \u003cp\u003eL: number of gestational age groups; there were 8 groups from 16\u003csup\u003e+ 0\u003c/sup\u003e to 23\u003csup\u003e+ 6\u003c/sup\u003e weeks of gestation.\u003c/p\u003e\n \u003cp\u003eZ\u003csub\u003e(1−α/2)\u003c/sub\u003e = 1.96, δ value = 0.025, x̅ : mean of UCA, \u003cem\u003eS\u003c/em\u003e: standard deviation. According to Dagdeviren et al. [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e], x̅ = 110.57 mm and \u003cem\u003eS\u003c/em\u003e = 13.46 mm. Based on these values, the minimum sample size was 729 subjects.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec5\"\u003e\n \u003ch2\u003eStudy population\u003c/h2\u003e\n \u003cp\u003eAll singleton pregnant women aged 18 to 40 years old and between 16\u003csup\u003e+ 0\u003c/sup\u003e and 23\u003csup\u003e+ 6\u003c/sup\u003e weeks of gestation with viable fetuses who were examined and managed at the Department of Pregnancy Management \u0026amp; Prenatal Diagnosis of Haiphong Hospital of Obstetrics and Gynecology between September 2019 and September 2020 were included in the study.\u003c/p\u003e\n \u003cp\u003eThe exclusion criteria were as follows: 1) a history of sPTB or second trimester miscarriage (miscarriage at 13\u003csup\u003e+ 0\u003c/sup\u003e-19\u003csup\u003e+ 6\u003c/sup\u003e weeks gestation) [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e], 2) a short CL (CL ≤ 25 mm), 3) signs of threatened miscarriage or preterm birth, 4) severe fetal malformations, 5) medically indicated preterm birth, 6) a cervical mass or previous cervical surgery, 7) the use of available preterm birth prevention methods (micronized progesterone, cerclage, cervical pessary), and 8) loss of follow-up.\u003c/p\u003e\n \u003cp\u003eA total of 1,165 pregnant women with singleton pregnancies at 16\u003csup\u003e+ 0\u003c/sup\u003e to 23\u003csup\u003e+ 6\u003c/sup\u003e weeks gestation were voluntary participants in this study and were recruited according to the recruitment guidelines. Each participant underwent TVS once for CL and UCA measurements and was followed-up until delivery. Women who delivered at other hospitals were contacted via telephone. After excluding 114 participants at high risk for sPTB or loss of follow-up, 1,051 pregnant women were included in the final analysis (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec6\"\u003e\n \u003ch2\u003eAssessment of cervical length and the uterocervical angle\u003c/h2\u003e\n \u003cp\u003eThe cervical length and uterocervical angle measurements were performed by a single sonographer who was certified and monitored by the Maternal Fetal Medicine Foundation. The ultrasound machines used for measurements were the Samsung Medison WS80A (Korea) and GE Voluson E6 (GE Healthcare Korea) with a transvaginal probe (frequency 4.0–9.0 MHz). Patients had an empty bladder, and excessive pressure on the cervix was avoided. The CL measurements were performed following the standard method of The Fetal Medicine Foundation, tracing a single straight line from the internal to external os. Because the guidelines for UCA are not yet established, the UCA was measured following previously published protocols, according to the method described by Dziadosz et al. [\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e]. In short, a first line is placed from the internal os to the external os irrespective of whether the cervix is straight or curved. A second line is then drawn to delineate the lower uterine segment. This ray is traced up the anterior uterine segment to a distance allowed by the preloaded image. Ideally, the second ray reaches 3 cm up the lower uterine segment to establish an adequate measurement. The angle between the two lines is the UCA value (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Each participant had three images measured to reduce measurement bias, and the most obtuse UCA from the three images was used. The patients’ demographic characteristics, ultrasound images, expected date of delivery, obstetric complications and perinatal outcome data were recorded.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec7\"\u003e\n \u003ch2\u003eOutcome measures\u003c/h2\u003e\n \u003cp\u003eThe mean difference in the uterocervical angles among pregnant women with term and preterm deliveries (before 37 weeks of gestation) was defined as the primary outcome parameter. The secondary outcome was the percentage of preterm birth women before 37 weeks that had UCA values lying on the 75th percentile curve.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec8\"\u003e\n \u003ch2\u003eStatistical analysis\u003c/h2\u003e\n \u003cp\u003eAll analyses were performed using SPSS version 26.0 (SPSS, Inc., Chicago, IL). Student’s t test was used to evaluate the difference between two means, and p \u0026lt; 0.05 was considered statistically significant. Calculating the correlation between two quantities according to each function y = f(x) (y is anthropometric quantities, x is gestational age), there was a correlation when r \u0026gt; 0.5. The distribution of UCA values was visualized using a scatter plot against gestational age. Predicted median and 5th and 95th percentiles of UCA values with 95% confidence intervals according to GA were estimated using quantile regression, which allows the possibility to detect whether the range of UCA values changes with GA, as well as the display of the confidence band around each percentile. Kurtosis and skewness calculations were performed to determine the distribution of cervical angle measurements according to gestational age. If there was a normal distribution, the values corresponding to the 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles were measured by the following formulas:\u003c/p\u003e\n \u003cp\u003e+ 25th, 75th percentile =\u0026nbsp;x̅ ± 1.88. SD\u003c/p\u003e\n \u003cp\u003e+ 5th, 95th percentile =\u0026nbsp;x̅ ± 1.645. SD\u003c/p\u003e\n \u003cp\u003e+ 10th, 90th percentile =\u0026nbsp;x̅ ± 1.28. SD\u003c/p\u003e\n \u003cp\u003e+ The 50th percentile =\u0026nbsp;x̅ = the result from solving a corresponding equation (with the highest r) and the corresponding values [\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eThe mean values were determined after solving the selective equation (with the highest r), and the values corresponding to the percentiles calculated according to the above formula were the basis for establishing the UCA percentile chart according to gestational age.\u003c/p\u003e\n \u003cp\u003eThe research proposal was approved by the Ethical Council in Biomedical Research of Hue University of Medicine and Pharmacy, Vietnam (Ethics Committee ID number H2020/035) and the Scientific Council of Haiphong Hospital of Obstetrics and Gynecology, Vietnam (IEC, 1186/QD-BVPSHP). All participants voluntarily signed a written informed consent form after hearing a full explanation of the purpose of this study.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 1,165 pregnant women were included in this cohort. During the follow-up period, 114 women at high risk for sPTB or loss to follow-up were identified and excluded from the final analysis. The exclusion criteria were as follows: short cervical length (22 women), history of sPTB (18 women), complete placental previa (5 women), placental abruption (2 women), severe preeclampsia (4 women), hydrops fetalis (2 women), severe fetal malformations (5 women), fetal chromosomal abnormality (2 with trisomy 21), fetal intrauterine growth restriction (5 women), serious thalassemia fetal (1 woman), fetal distress (4 women), amniotic fluid infection (1 woman), previous cervical surgery (2 women), the use of available preterm birth prevention methods (micronized progesterone, cerclage, cervical pessary) (20 women), and loss to follow-up (21 women). Overall, 1,051 pregnant women who met the study criteria were divided into two groups: a full-term delivery group (\u0026ge;\u0026thinsp;37 weeks, 988 women) and a preterm delivery group (before 37 weeks, 63 women). A full comparison of the demographic and clinical data of the two groups is presented in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The mean UCA value increased with GA from 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e), and the difference was statistically significant (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eStudy subjects\u0026rsquo; characteristics.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCharacteristics\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eFull-term delivery\u003c/p\u003e\n\u003cp\u003e(\u0026ge;\u0026thinsp;37 weeks)\u003c/p\u003e\n\u003cp\u003e(n\u0026thinsp;=\u0026thinsp;988)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ePreterm birth\u003c/p\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;37 weeks\u003c/p\u003e\n\u003cp\u003e(n\u0026thinsp;=\u0026thinsp;63)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eP value\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth colspan=\"4\" align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eMaternal characteristics\u003c/em\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAge (years)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e28.83\u0026thinsp;\u0026plusmn;\u0026thinsp;5.06\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e29.19\u0026thinsp;\u0026plusmn;\u0026thinsp;5.02\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.5913\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eBMI (kg/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20.53\u0026thinsp;\u0026plusmn;\u0026thinsp;2.51\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20.37\u0026thinsp;\u0026plusmn;\u0026thinsp;2.07\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.676\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eParity\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.2685\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eGestational age at TVS (weeks)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e19.74\u0026thinsp;\u0026plusmn;\u0026thinsp;2.31\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20.90\u0026thinsp;\u0026plusmn;\u0026thinsp;1.79\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCL (mm)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e36.52\u0026thinsp;\u0026plusmn;\u0026thinsp;5.07\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e32.05\u0026thinsp;\u0026plusmn;\u0026thinsp;4.37\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eUCA (degrees)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e83.80\u0026thinsp;\u0026plusmn;\u0026thinsp;24.18\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e117.86\u0026thinsp;\u0026plusmn;\u0026thinsp;20.25\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eUCA \u0026ge; 95\u003csup\u003eo\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e309 (31.3%)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e56 (88.9%)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"4\" align=\"left\"\u003e\n\u003cp\u003e\u003cspan class=\"BoldItalic\"\u003eNeonatal characteristics and outcomes\u003c/span\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eGestational age at birth (weeks)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e38.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.90\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.36\u0026thinsp;\u0026plusmn;\u0026thinsp;2.01\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eBirthweight (gram)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3182.79\u0026thinsp;\u0026plusmn;\u0026thinsp;285.42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2412.69\u0026thinsp;\u0026plusmn;\u0026thinsp;480.42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eC-section\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e410 (41.5%)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8 (12.7)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eNICU admission\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34 (3.44)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e33(54.10)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eDeaths\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eMean value of the UCA at 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eGA\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eN\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMean\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eSD\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e6\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e17\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e7\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e18\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e8\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e19\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e9\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e20\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e0\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e21\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e1\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e22\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e2\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e23\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e3\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e112\u003c/p\u003e\n\u003cp\u003e110\u003c/p\u003e\n\u003cp\u003e149\u003c/p\u003e\n\u003cp\u003e82\u003c/p\u003e\n\u003cp\u003e110\u003c/p\u003e\n\u003cp\u003e145\u003c/p\u003e\n\u003cp\u003e215\u003c/p\u003e\n\u003cp\u003e128\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e74.65\u003c/p\u003e\n\u003cp\u003e79.15\u003c/p\u003e\n\u003cp\u003e81.07\u003c/p\u003e\n\u003cp\u003e88.30\u003c/p\u003e\n\u003cp\u003e86.96\u003c/p\u003e\n\u003cp\u003e90.71\u003c/p\u003e\n\u003cp\u003e89.82\u003c/p\u003e\n\u003cp\u003e92.21\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.19\u003c/p\u003e\n\u003cp\u003e24.76\u003c/p\u003e\n\u003cp\u003e27.32\u003c/p\u003e\n\u003cp\u003e20.05\u003c/p\u003e\n\u003cp\u003e24.15\u003c/p\u003e\n\u003cp\u003e23.22\u003c/p\u003e\n\u003cp\u003e26.93\u003c/p\u003e\n\u003cp\u003e24.32\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd colspan=\"3\" align=\"left\"\u003e\n\u003cp\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eIn the preterm birth group, the mean CL was significantly shorter (36.52\u0026thinsp;\u0026plusmn;\u0026thinsp;5.07 mm vs. 32.05\u0026thinsp;\u0026plusmn;\u0026thinsp;4.37 mm, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), and the mean UCA value was significantly wider than those in the full-term group (83.80\u0026thinsp;\u0026plusmn;\u0026thinsp;24.18\u0026deg; vs. 117.86\u0026thinsp;\u0026plusmn;\u0026thinsp;20.25\u0026deg;) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). There was no significant difference between the two groups in regard to age, BMI, parity, and the cesarean rate (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e\n\u003cp\u003eTo determine the distribution characteristics of observed values in each gestational age subgroup, we calculated the Kurtosis coefficient and skewness coefficient, which proves that the distribution is normal when the Kurtosis coefficient\u0026thinsp;\u0026le;\u0026thinsp;\u0026plusmn;\u0026thinsp;2 and skewness coefficient\u0026thinsp;\u0026le;\u0026thinsp;\u0026plusmn;\u0026thinsp;2. These distribution characteristics were determined to calculate the values corresponding to the percentile curve. If the distribution was normal, the percentile curve was measured by the following formula: percentile curve =\u0026nbsp;x̅ \u0026plusmn; k.SD. The results of the Kurtosis coefficient and skewness coefficient of the UCA value according to GA subgroups are described in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eKurtosis coefficient and skewness coefficient of the UCA at 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eGA\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eKurtosis coefficient\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eSkewness coefficient\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e6\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e17\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e7\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e18\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e8\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e19\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e9\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e20\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e0\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e21\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e1\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e22\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e2\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e23\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e3\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.247\u003c/p\u003e\n\u003cp\u003e0.550\u003c/p\u003e\n\u003cp\u003e0.092\u003c/p\u003e\n\u003cp\u003e0.430\u003c/p\u003e\n\u003cp\u003e0.345\u003c/p\u003e\n\u003cp\u003e0.119\u003c/p\u003e\n\u003cp\u003e0.322\u003c/p\u003e\n\u003cp\u003e0.071\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.281\u003c/p\u003e\n\u003cp\u003e1.193\u003c/p\u003e\n\u003cp\u003e0.318\u003c/p\u003e\n\u003cp\u003e0.783\u003c/p\u003e\n\u003cp\u003e0.168\u003c/p\u003e\n\u003cp\u003e-0.149\u003c/p\u003e\n\u003cp\u003e1.384\u003c/p\u003e\n\u003cp\u003e0.095\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eTo demonstrate and determine the rule of the UCA measurement variation with a GA from 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks, we determined the relationship between the UCA value (y) and GA (x) according to a linear function, a quadratic function and a cubic function. The function with the highest correlation coefficient correctly represented the variation rule of UCA values, which was the cubic function (with r\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.051). The line representing the UCA variation rule connects the mean values after solving the cubic function, y = -81.11x\u0026thinsp;+\u0026thinsp;13.65x \u0026ndash; 0.27x\u003csup\u003e2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eBased on the above function representing the selected variation rule, Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e presents the mean values and corresponding values for the 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentile curves.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab4\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eGA-based UCAs corresponding to the 5th, 10th, 25th, 50th, 75th, 90th, and 95th .\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eGA\u003c/p\u003e\n\u003c/th\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eN\u003c/p\u003e\n\u003c/th\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eSD\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"7\" align=\"left\"\u003e\n\u003cp\u003eDistribution of UCA values according to percentile\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e5%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e10%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e25%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e50%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e75%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e90%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e95%\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e6\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e112\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.19\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e39.82\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e48.11\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e59.32\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e73.55\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e88.62\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e104.64\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e114.10\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e17\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e7\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e110\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e24.76\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e45.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e50.73\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e61.14\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e79.59\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e91.79\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e105.94\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e127.75\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e18\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e8\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e149\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e27.32\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e30.03\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e45.32\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e64.80\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e79.86\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e100.39\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e114.50\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e124.44\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e19\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;1\u003c/strong\u003e9\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e82\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20.05\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e58.23\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e66.28\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e73.17\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e85.60\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e101.31\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e113.52\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e125.20\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e0\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e110\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e24.15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e48.72\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e56.00\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e70.90\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e85.68\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e102.07\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e119.73\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e132.69\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e21\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e1\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e145\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e23.22\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e52.53\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e59.58\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e74.90\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e87.93\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e106.28\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e119.33\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e131.28\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e2\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e215\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e26.93\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e44.30\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e57.84\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e72.44\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e90.37\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e105.14\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e122.35\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e128.48\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e23\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u003cstrong\u003e\u0026minus;\u0026thinsp;2\u003c/strong\u003e3\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e128\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e24.32\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e53.00\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e60.84\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e75.24\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e91.20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e109.58\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e122.83\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e132.56\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eLinear regression analysis showed a significant change in the range of UCA values from 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks of gestation (increase of 2.51 degrees per week, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The range of the UCA at the 5th to 95th percentile ranges from 38.96\u0026deg; (95% CI, 35.45\u0026deg;- 44.31\u0026deg;) to 133.70\u0026deg; (95% CI, 128.92\u0026deg;- 139.32\u0026deg;).\u003c/p\u003e\n\u003cp\u003eThere were 42/63 women with preterm birth before 37 weeks with a UCA value above the 90th percentile and 53/53 women with preterm birth before 37 weeks with a UCA value\u0026thinsp;\u0026ge;\u0026thinsp;95\u0026deg;, accounting for 66.7% and 84.1%, respectively (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eOur study of 1,051 singleton pregnant women at 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation with low risk for sPTB who were treated at Haiphong Hospital of Obstetrics and Gynecology from September 2019 to September 2020 showed that the normal range of UCA values at the 5th to 95th percentile was from 46.47\u0026deg; (95% CI, 40.27\u0026deg; \u0026minus;\u0026thinsp;51.81\u0026deg;) to 127.06\u0026deg; (95% CI, 123.02\u0026deg; \u0026minus;\u0026thinsp;130.71\u0026deg;) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), with significant changes during this GA period (increase of 2.51 degrees per week, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Similarly, the study of Llobet et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] with 275 singleton pregnant women showed that the mean UCA values increased from the first to the second trimester with statistical significance (84.2\u0026deg; versus 94.5\u0026deg;, p\u0026thinsp;=\u0026thinsp;0.019). Sawaddisan et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] (Thailand, 2020) studied 372 singleton pregnant women at GAs from 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks and showed that UCA values changed according to GA, but this change was not statistically significant (increase of 0.3\u0026deg; per week, p\u0026thinsp;=\u0026thinsp;0.757).\u003c/p\u003e \u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the mean values of the UCA in the preterm birth before 37 weeks group were significantly wider than those in the full-term delivery group (83.80\u0026deg; \u0026plusmn; 24.18\u0026deg; vs. 117.86\u0026deg; \u0026plusmn; 20.25\u0026deg;, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Sochacki-Wojcicka et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] also found that there was a statistically significant difference in the mean UCA value between the preterm birth group and the full-term delivery group in the first trimester (115.5\u0026deg; vs. 85\u0026deg;, p\u0026thinsp;=\u0026thinsp;0.0002) and 2nd trimester (126\u0026deg; vs. 91.5\u0026deg;, p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001). The study of Llobet et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] with the aim of determining the correlation of the cervical angle with preterm birth also concluded that the UCA in the second trimester in the preterm birth group was wider than that in the full-term delivery group [(105.16\u0026deg; vs. 94.53\u0026deg;, p\u0026thinsp;=\u0026thinsp;0.015, RR\u0026thinsp;=\u0026thinsp;0.821 (95% CI, 0.74\u0026ndash;0.97)]. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e also demonstrates that the rate of preterm birth before 37 weeks in our study was 6% (63/1051 women). The majority of women with preterm birth had a UCA\u0026thinsp;\u0026ge;\u0026thinsp;95\u0026deg; compared with those with full-term delivery (88.9% vs. 31.3%, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eRecently, several studies have shown that the UCA can be useful in predicting sPTB [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Dziadosz et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] observed that second trimester UCA measurement could detect the possibility of preterm birth at \u0026lt;\u0026thinsp;37 weeks with a sensitivity of 80% when the angle was \u0026ge;\u0026thinsp;95\u0026deg; and at \u0026lt;\u0026thinsp;34 weeks with a sensitivity of 81% when the UCA was \u0026ge;\u0026thinsp;105\u0026deg;. The same authors also reported that when they performed stepwise linear regression analysis, the UCA was dependent on maternal age, obesity at conception, nulliparity, and race. Lynch et al. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] also found that a UCA\u0026thinsp;\u0026ge;\u0026thinsp;105\u0026deg; at 19 to 25 weeks gestation was associated with the risk of preterm birth before 37 weeks; however, only pregnant women with a short cervix\u0026thinsp;\u0026le;\u0026thinsp;25 mm were included in this study. A recent study by Singh et al. [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] also revealed that the risk of spontaneous preterm delivery was higher in women with obtuse UCAs (\u0026ge;\u0026thinsp;95 degrees), with a sensitivity of 86.7%, specificity of 93.0%, positive predictive value of 83.0%, and negative predictive value of 94.6%. It can be explained that if the UCA is obtuse, the gravity of the uterus and the fetus acting on the internal os tend to be along the direction of the cervix, which can lead to shortening of the cervix, and this is one of the factors causing preterm birth. Therefore, the function of cervical cerclage based on this mechanism is not only to support the cervix to evenly distribute the force from the uterus but also to change the UCA from obtuse to acute, changing the force of the uterus to the posterior fornix to avoid shortening the cervix. This has been proven through the study of Cannie et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. They analyzed CL and UCA measurements in 2 groups of pregnant women: 198 women with no high risk of preterm birth and 73 women with a high risk of preterm birth who had an Arabin pessary at 14 to 33 weeks gestation. The authors performed cervical magnetic resonance imaging before inserting the Arabin pessary and monthly follow-up until the pessary was removed. The results showed that in the group of pregnant women with a low risk of PTB, the UCA measurement did not change, but the CL values decreased significantly with GA (r\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.15, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In the high-risk preterm birth group, 63 patients who delivered after 34 weeks had a mean UCA value that was significantly reduced compared to that before the Arabin pessary was inserted (132\u0026deg; vs. 146\u0026deg;, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01), but it did not change in the 8 patients who delivered before 34 weeks (143\u0026deg; vs. 152\u0026deg;, p\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003eTo demonstrate the clinical applicability of the established UCA percentile chart, we performed the distribution of UCA in the PTB before 37 weeks gestation group on the percentile chart of the singleton pregnant woman at 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), and we found that most of the women with preterm birth before 37 weeks had a UCA value above the 75th percentile (42/63 women, accounting for 66.7%). Based on the results of this study, we have the same opinion as some authors that the UCA values in women with PTB is wider than that in women with term delivery. Preterm birth rates are increased in women with obtuse uterocervical angles. Thus, should we consider the 75th percentile on the above UCA percentile chart as a limit to predict PTB before 37 weeks in pregnant women at low risk for preterm delivery? More in-depth studies with a large sample size are necessary to prove the prognostic value of UCA measurements in the prediction of preterm birth, especially in combination with a short cervical length.\u003c/p\u003e \u003cp\u003eIn clinical practice, measuring the CL by TVS at 16\u0026ndash;24 weeks gestation is the current recommended screening method for preterm birth (SMFM, ACOG, ISUOG) [\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Measuring the UCA and CL (16\u0026ndash;24 weeks) by vaginal ultrasound at the same time can increase the efficiency of preterm birth screening; additionally, it is convenient and saves money to measure both of these parameters at the same time in pregnancy.\u003c/p\u003e \u003cp\u003eThis study had three major strengths. First, this is the first study in Vietnam to establish the percentile chart of UCA measurements in singleton pregnant women at 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation with low risk for sPTB. Second, the measurement of all uterocervical angles was performed by a single obstetrician to control for interobserver variability, and the prospective nature of the study to control for the risk of information bias, focusing on investigating the UCA values of a large study sample, can also be considered strengths of the study. Third, the study subjects included only pregnant women at low risk for sPTB (without a history of sPTB or short cervical length), which could have eliminated the role and impact of these factors on pregnancy outcomes. However, the present study had several limitations. First, women with several maternal conditions that predispose women to sPTB, such as a history of sPTB, short cervical length, and previous cervical surgery, were excluded from the study sample, limiting the representativeness of the general population of pregnant women. Second, selecting pregnant women from a single center can affect the generalizability of our findings.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eOur findings provided baseline information about the normal range of UCA values in singleton pregnant women at 6\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks with low risk for sPTB. The range of UCA values at the 5th to 95th percentile ranged from 46.47 degrees (95% CI, 40.27\u0026deg; \u0026minus;\u0026thinsp;51.81\u0026deg;) to 127.06 degrees (95% CI, 123.02\u0026deg; \u0026minus;\u0026thinsp;130.71\u0026deg;). There was a significant change in the range of UCA values from 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation in singleton pregnant women at low risk for sPTB (increase of 2.51 degrees per week, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eThe values of the UCA in the preterm birth before 37 weeks group was significantly wider than that in the full-term delivery group (117.86\u0026deg; \u0026plusmn; 20.25\u0026deg; vs. 83.80\u0026deg; \u0026plusmn; 24.18\u0026deg;, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and the majority of women with preterm birth had a UCA value\u0026thinsp;\u0026ge;\u0026thinsp;95\u0026deg; compared with those with full-term delivery (88.9% vs. 31.3%, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Most of the women with preterm birth before 37 weeks had a UCA value\u0026thinsp;\u0026ge;\u0026thinsp;95\u0026deg; (53/63 women, accounting for 84.1%) and above the 75th percentile (42/63 women, accounting for 66.7%). Therefore, it is advisable to monitor the UCA, especially in pregnant women with a UCA value\u0026thinsp;\u0026ge;\u0026thinsp;95\u0026deg; at 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e to 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks of gestation.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eCL: Cervical length\u003c/p\u003e\n\u003cp\u003eUCA: Uterocervical angle\u003c/p\u003e\n\u003cp\u003eTVS: Transvaginal ultrasonography\u003c/p\u003e\n\u003cp\u003ePTB: Preterm birth\u003c/p\u003e\n\u003cp\u003esPTB: Spontaneous preterm birth\u003c/p\u003e\n\u003cp\u003eGA: Gestational age\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eEthics approval and consent to participate\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe research proposal was approved by the Ethical Council in Biomedical Research of Hue University of Medicine and Pharmacy, Vietnam (Ethics Committee ID number H2020/035) and the Scientific Council of Haiphong Hospital of Obstetrics and Gynecology, Vietnam (IEC, 1186/QD-BVPSHP). All participants voluntarily signed a written informed consent form after hearing a full explanation of the purpose of this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eConsent for publication\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAvailability of data and materials\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eCompeting interests\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFunding\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research did not receive specific grants from funding agencies in the public, commercial or nonprofit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAuthors\u0026apos; contributions\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eN.T.H.T., V.V.T. and N.V.Q.H. designed the study. N.T.H.T. and V.V.T. performed data collection. N.T.H.T. and N.V.Q.H. performed statistical analyses and wrote the first manuscript. N.T.H.T., V.V.T. and N.V.Q.H. critically revised successive drafts of the paper. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAcknowledgements\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank all the pregnant women who agreed to participate in this study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDe Costa A, Moller AB, Blencowe H, Johansson EW, Hussain-Alkhateeb L, Ohuma EO, et al. Study protocol for WHO and UNICEF estimates of global, regional, and national preterm birth rates for 2010 to 2019. PLoS ONE. 2021;16:e0258751.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChawanpaiboon S, Vogel JP, Moller AB, Lumbiganon P, Petzold M, Hogan D, et al. 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Obstet Gynecol. 2021;138:e65\u0026ndash;90.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"bmc-pregnancy-and-childbirth","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prch","sideBox":"Learn more about [BMC Pregnancy and Childbirth](http://bmcpregnancychildbirth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/prch/default.aspx","title":"BMC Pregnancy and Childbirth","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"uterocervical angle (UCA), singleton pregnancy, preterm birth","lastPublishedDoi":"10.21203/rs.3.rs-2406007/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2406007/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Background: Cervical length (CL) measured by ultrasound in the second trimester is a predictor of spontaneous preterm birth (sPTB). The uterocervical angle (UCA) has recently been investigated as a parameter to identify women at risk of sPTB. This study aimed to investigate the UCAs’ distribution in singleton pregnant women at 16+0-23+6 weeks of gestation with low risk for sPTB.\nMethods: This was a prospective cohort study of 1,051 pregnant women with singleton pregnancies at low risk for preterm delivery. Pregnant women with a viable singleton fetus at 16+0-23+6 weeks of gestation were enrolled in the study conducted at the Haiphong Hospital of Obstetrics and Gynecology, Vietnam, from 09/2019 to 09/2020.\nCL and the UCA were assessed using transvaginal ultrasonography (TVS) by a single sonographer. Subjects were followed-up until the end of pregnancy, and maternal and neonatal outcomes were recorded. The UCAs’ range and their relationship with gestational age were evaluated using regression analysis. P\u003c0.05 was considered statistically significant.\nResults: The normal range of the UCA (5th-95th percentiles) was 46.47° (95% CI, 40.27°-51.81°) to 127.06° (95% CI, 123.02°-130.71°). The UCAs in the preterm birth (\u003c37 weeks) and full-term groups were 117.86°±20.25° and 83.80°±24.18°, respectively (p\u003c0.001). Linear regression analysis showed a significant change in the UCA range from 16+0 to 23+6 weeks of gestation (2.51 degrees per week, p\u003c0.001). The quadratic function yielded the highest correlation coefficient in the variation rule of the UCA values (r2=0.051). A total of 42/63 (66.7%) patients with preterm birth \u003c37 weeks had a UCA above the 75th percentile. The rate of UCA values ≥95° was significantly higher in the sPTB group than in full-term delivery group (88.9% vs. 31.3%, p\u003c0.001).\nConclusions: The UCA values in the preterm birth \u003c37 weeks group were significantly wider in the full-term delivery group (p\u003c0.001), and the majority of women with preterm birth had an UCA ≥ 95° compared with those with full-term delivery (p\u003c0.001). It is advisable to monitor the UCA, especially in pregnant women with a UCA value ≥ 95° at 16+0-23+6 weeks of gestation.","manuscriptTitle":"Distribution of uterocervical angles of pregnant women at 16+0 to 23+6 weeks gestation with low risk for preterm delivery: First Vietnamese cohort of women with singleton pregnancies","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-01-04 22:06:59","doi":"10.21203/rs.3.rs-2406007/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2023-01-31T06:09:16+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2023-01-21T08:54:08+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"19193763-3a5e-4a4f-a0a4-62d8c84492d2_SNPRID","date":"2023-01-09T08:40:49+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-01-09T06:43:31+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-01-03T06:24:44+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2022-12-30T17:07:36+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2022-12-30T17:03:28+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Pregnancy and Childbirth","date":"2022-12-22T16:18:24+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-pregnancy-and-childbirth","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prch","sideBox":"Learn more about [BMC Pregnancy and Childbirth](http://bmcpregnancychildbirth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/prch/default.aspx","title":"BMC Pregnancy and Childbirth","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"be707f1e-45dd-430e-a9b9-242810b64d7c","owner":[],"postedDate":"January 4th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-10-16T20:49:39+00:00","versionOfRecord":{"articleIdentity":"rs-2406007","link":"https://doi.org/10.1186/s12884-023-05597-3","journal":{"identity":"bmc-pregnancy-and-childbirth","isVorOnly":false,"title":"BMC Pregnancy and Childbirth"},"publishedOn":"2023-04-28 20:35:31","publishedOnDateReadable":"April 28th, 2023"},"versionCreatedAt":"2023-01-04 22:06:59","video":"","vorDoi":"10.1186/s12884-023-05597-3","vorDoiUrl":"https://doi.org/10.1186/s12884-023-05597-3","workflowStages":[]},"version":"v1","identity":"rs-2406007","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2406007","identity":"rs-2406007","version":["v1"]},"buildId":"GqpaHPwrfC8PjnIFayRh5","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}