{"paper_id":"d3ba832d-699e-4550-a634-135a5d01aa6b","body_text":"Follicular aspiration in  in vitro  fertilization (IVF) treatments is\nscheduled 36 hours (h) after triggering with an ovulation inductor. This trigger\ninduces an  in vivo  resumption of the first meiosis in those oocytes\npresent inside preovulatory follicles ( Abbara\n et al ., 2018 ). Currently, pituitary suppressors are\noften prescribed to avoid spontaneous ovulation prior to trigger administration\n( Diedrich  et al ., 1994 ).\nIn some cases however, a dominant follicle partially ruptures prematurely and prior\nto the scheduled hour for follicular aspiration.\nIn our case, we refer to “partial premature ovulation” (PPO) when this phenomenon is\nobserved by ultrasound while the oocyte pick-up (OPU) procedure is being performed.\nWe thus called it if there was a soon-to-be-formed corpus luteum structure or a low\nfollicular count than expected in the last ultrasound performed prior to OPU, with\nboth conditions in association or not with free fluid in the pouch of Douglas.\nIn some cases, a prematurely ruptured dominant follicle does not mean that the oocyte\nenclosed inside it has been expelled, which has been previously described in the\nliterature ( Craft  et al .,\n1980 ;  Stanger & Yovich, 1984 ).\nFurthermore  Teramoto  et al. \n(2019)  not only demonstrated that oocytes can be retrieved from this type\nof follicles, but also proved their competence.\nHowever, one of the main concerns about this phenomenon is the competence of the\nwhole retrieved oocyte cohort after it is detected. It would be logical to think\nthat the oocytes retrieved from these ruptured follicles, if obtained, may be in a\ndifferent maturity stage and may, thus, be less competent. Moreover, partial\novulation may have induced a dominance phenomenon in the rest of the cohort, which\nleads them to the atresia, or at least to an impaired final maturation process\n( Son  et al ., 2011 ).\nPartial ovulation has not been extensively studied in the literature. In this\nretrospective study, we aim to describe our own experience in an infertility clinic\nin Spain regarding such cases. We analyze the frequency of this event, the number of\nretrieved oocytes once detected, and the maturation, fertilization, blastocyst\nformation and pregnancy rates related to these oocytes. We also aim to assess if\nthere is any potential early predictor of PPO that could provide us with an early\nindication of its occurrence.\n\nA retrospective study performed at an infertility clinic in Spain between 2016\nand 2021. It includes all the patients submitted to a follicular aspiration\nprocedure after a controlled ovarian stimulation protocol for IVF treatment.\nFemale patients having undergone follicular aspiration for IVF treatment after\ncontrolled ovarian stimulation treatment and during the study period, regardless\nof semen origin. Mixed cycles with both aspirated and thawed oocytes, as well as\noocyte donation cycles and oocyte vitrification cycles, were excluded from the\nanalysis.\nOvarian stimulation was performed following the routine clinical practice in\nIVIRMA Valencia, as described elsewhere ( Giles\n et al ., 2021 ;  Melo  et al ., 2009 ). Ovulation induction was\ntriggered when 3 or more follicles ≥18 mm were confirmed by transvaginal\nultrasound, using the gonadotropin releasing hormone (GnRH) agonist\n(Decapeptyl ® , Ipsen Pharma, France), the human chorionic\ngonadotropin (hCG) (Ovitrelle ® , Merck & Co., Inc, USA) or\nthrough the combined action of both of them.\nFollicular aspiration was carried out under sedation and transvaginally\nultrasound-guided 36 hours after administration of the ovulation trigger.\nPatients with premature partial ovulation (PPO) were detected by the clinician\nduring the follicular aspiration procedure and registered in the patient’s\nclinical history. The concept of PPO refers to the event in which the extrusion\nof the oocyte by the follicle, or at least the beginning of the ovulation\nprocess, happens earlier than expected according to protocol (prior to 36 hours\nafter ovulation induction). In addition, we call it partial ovulation because it\noccurs in only part of the follicles, not the entire cohort. Diagnosis was based\non the presence of soon-to-be-formed corpus luteum structure/s and/or a lower\nfollicular count than expected compared to the last ultrasound performed prior\nto OPU, and in association or not with free fluid in the pouch of Douglas.\nAround 80% of cases were evaluated by the same clinician because all the OPUs\nperformed in the clinic are done by the same gynecologist. Only the OPUs\nscheduled at weekends and during holidays were done by the gynecologist in\ncharge of on-call duty.\nThere was no traceability for the follicle of origin of the retrieved oocytes.\nHence, unlike  Teramoto  et al .,\n2019 , we cannot affirm if the retrieved oocytes came from the\nruptured follicles in PPO cycles.\nThe oocytes retrieved during follicular aspiration were denuded 4 h after the\nprocedure. After denudation, mature oocytes (metaphase II) were those with an\nextruded first polar body and no germinal vesicle visible in the cytoplasm. The\naspiration rate was defined as the number of retrieved oocytes per number of\nfollicles in the last ultrasound performed before pick-up. The maturation rate\nwas defined as the number of mature oocytes per total number of oocytes.\nOnly the mature oocytes were fertilized by intracytoplasmic sperm injection\n(ICSI). The fertilization rate was defined by the number of correctly fertilized\noocytes per total number of fertilized oocytes. Correctly fertilized oocytes\nwere those with two pronuclei and two polar bodies 17 h after fertilization.\nThe correctly fertilized oocytes were cultured  in vitro  until\nthe blastocyst stage on day 5 or 6 of development. Embryo quality was classified\nas A, B or C following the classification of the Spanish Association for the\nStudy of Reproduction Biology (ASEBIR) ( Pons,\n2015 ). Embryo quality was assessed by one of the 15 senior\nembryologists who make up the team of embryologists in the clinic.\nThe top-quality blastocyst rate was defined by the number of top-quality\nblastocysts per total number of available blastocysts. The top-quality\nblastocysts were those classified as A or B. In the pre-implantational genetic\ntesting for aneuploidies (PGT-A) cycles, the top-quality blastocysts were\nconsidered only those classified as A or B, which were also euploid.\nEmbryo transfer (ET) was performed on day 5 or 6 of development by senior\ngynecologists with transabdominal ultrasound guidance.\nThe biochemical pregnancy outcome was determined by a positive β-hCG test\n(serum levels of β-hCG >10 IU/ml 11 days after ET). Clinical pregnancy\nwas defined as the presence of at least one gestational sac upon ultrasound.\nOngoing pregnancy was defined as the presence of at least one viable fetus\nbeyond week 12, and live birth when pregnancy resulted in at least one live born\nneonate. The biochemical miscarriage rate was defined as a positive b-hCG test\nwith no evidence for a gestational sac and clinical miscarriage after confirming\nan intrauterine gestational sac. Ectopic pregnancy was defined as a gestational\nsac located outside the uterine cavity. The cumulative ongoing pregnancy rate\nafter the first, second, third and fourth ET attempt was also calculated.\nThe data from the women with PPO were compared to a matched control sample of\ncycles without partial ovulation during the same study period. A proportion of\n1:3 (PPO: nonPPO) was used. Matching was performed with RStudio through the\nlibrary “MatchIt” following the nearest neighbor method on the propensity score,\nwhich selects patients with the most similarity in the variables used for\nmatching. Cycles were matched for age, BMI, treatment year, performed embryo\ngenetic analysis and stimulation protocol type.\nThe numeric variables are shown as mean±standard deviation and were\ncompared by an ANOVA test. For the numeric variables with a negative homogeneity\nof variances test, a Mann-Whitney test was performed instead. The categorical\nvariables were shown by proportion and compared by the Chi-square test.\nA power analysis was run to compare the mean number of top-quality blastocysts\n(0.982), and the mean top-quality blastocyst rate (0.487), between the PPO and\nnonPPO groups to indicate the power of each comparison given our sample size.\nThe power analysis was calculated for these two variables because they account\nfor the final main IVF treatment outcome before ET. A power analysis was also\nperformed to compare pregnancy rates to indicate the statistical power of\npregnancy outcomes given the small sample size and the few ETs that derived from\nthe cycles included in this study. It showed powers of 0.298 for the comparison\nof the biochemical pregnancy rate, 0.166 for the clinical pregnancy rate and\n0.050 for the comparison of the ongoing pregnancy rate.\n\nDuring the study period, 8801 ovarian stimulation cycles for IVF treatment with\nfresh own oocytes were performed. PPO was detected in 117 of these cycles, which\nled to the occurrence of < 2% in our study population.\nThe cycles with no aspirated oocyte were excluded from the subsequent analysis to\nobtain a fair overview of embryological results. For this reason, 204 cycles of\nthe control group and two cycles from the PPO were excluded. There were four\nwomen with PPO in which OPU was not performed once ovulation had been detected\n(final n=8591).\nIn this population, 111 PPO cases were detected. The data from these cycles were\ncompared to a matched control sample of cycles without PPO (n=333) (PPO 1:3\nnonPPO) ( Figure 1 ).\nFigure 1 Flow chart of the IVF cycles included. PPO = premature partial\novulation. OPU = oocyte pick-up.\nFlow chart of the IVF cycles included. PPO = premature partial\novulation. OPU = oocyte pick-up.\nNo statistically significant difference in cycle characteristics was found, nor\nin the ovarian stimulation protocol prior to OPU ( Table 1 ) between the PPO and nonPPO groups.\nBaseline and cycle characteristics of the overall population (n=444) and\neach group (control  vs . PPO group). The overall data\nare shown in the first column, while columns 2 and 3 contain the data\nthat refer to each group and their comparison. The numeric variables are\nshown as mean±standard deviation. A  p  value\nrefers to the comparison using an ANOVA test.  MW Mann-Whitney\ntest due to a negative homogeneity of variances test; non-parametric\ndata are shown by median±interquartile range. The categorical\nvariables are shown as proportion. A  p  value refers to\nthe comparison using the Chi-square test.\n * p ≤0.05 was considered statistically\nsignificant. BMI = body mass index; AMH = antimullerian hormone; PGT-A =\npre-implantational genetic testing for aneuploidies. PPO = partial\npremature ovulation. FSH = follicle stimulating hormone. hMG = human\nmenopausal gonadotropin. hCG = human chorionic gonadotropin. GnRh-a =\ngonadotropin releasing hormone agonist. E2 = estradiol. P4=\nprogesterone. IQR = interquartile range.\nThe variables related to oocyte quantity were significantly lower in the PPO\npatients than in the nonPPO patients. The variables related to oocyte quality\nwere similar among groups ( Table 2 ).\nThe oocyte quantity and quality variables in the overall population\n(n=444) and each group (PPO vs. control group). The numeric variables\nare shown as mean ± standard deviation. A  p \nvalue refers to the comparison using an ANOVA test.\n MW Mann-Whitney Test due to a negative homogeneity of\nvariances test; non-parametric data are shown by\nmedian±interquartile range. The categorical variables are shown\nas proportion. A p value refers to the comparison using the Chi-square\ntest.  * p ≤0.05 was considered\nstatistically significant. PPO = partial premature ovulation. IQR =\ninterquartile range.\nIn all, 154 ETs of 95 patients were performed. Of these, 17 ETs accounted for PPO\ncycles from 12 patients and 137 ETs for the control group cycles of 83\npatients.\nETs were fresh in 35.7% of cases (55) and frozen in the remaining 64.3% (99).\nFrozen ETs were performed in the natural cycle context in 16.2% of cases (16)\nand in 83.8% (83) of cases. A PGT-A analysis was performed in 4.0% of the frozen\nET cases (4).\nThere were no significant differences among groups for any variable related to ET\nand pregnancy results ( Table 3 ).\nMain characteristics of the performed ETs in the overall population\n(n=444) and the comparison between the PPO and control groups. The\nnumeric variables are shown as mean ± standard deviation. A p\nvalue refers to the comparison using an ANOVA test. The categorical\nvariables are shown by proportion. A  p  value refers to\nthe comparison using the Chi-square test.  * p \n≤ 0.05 was considered statistically significant. ET = embryo\ntransfer; PPO = partial premature ovulation.\nTable 1  shows that the only significantly\ndifferent variables in the PPO and control groups were the type of trigger, as\nwell as E2 and P4 levels on the triggering day. Cycles in the PPO group have\nhigher E2 and P4 levels on the triggering day, and triggered with higher\nfrequency using the GnRH agonist.\nThe adjusted binary logistic regression model for the phenomenon of PPO is shown\nin  Table 4 .\nAdjusted binary logistic regression model for the phenomenon of premature\npartial ovulation (PPO). Confounding factors in the first half table are\nserum E2 and P4 levels on the triggering day, as well as triggering with\nGnRH-a  vs . hCG or hCG and GnRH-a; in the second half\ntable are serum E2 levels, P4 levels ≥ 1.5 ng/ml\n vs . levels below this cut-off and triggering with\nGnRh-a.  * p ≤0.05 was considered\nstatistically significant. hCG = human chorionic gonadotropin. GnRH-a =\ngonadotropin releasing hormone agonist. E2 = estradiol. P4 =\nprogesterone. CI = confidence interval.\nRegarding the P4 levels, those of 13.6% of the overall population were over the\ncut-off point of 1.5ng/ml ( Bosch  et\nal ., 2010 ) on the triggering day. Of these, 38.5%\nexhibited PPO, while 61.5% were from the control group\n( p <0.001). In the PPO group, 28.8% of patients had serum P4\nlevels ≥1.5ng/ml  vs.  10.2% in the control group\n( p <0.001). The adjusted binary logistic regression model\nfor the phenomenon of PPO taking into consideration the variable serum P4 levels\non the triggering day as categorical (yes  vs . no) is shown in\n Table 4 .\nThe P4 levels above the cut-off point were related to: a significantly larger\nmean number of follicles in the last ultrasound performed before OPU\n(14.4±5.8  vs.  11.6±5.4 in the group of patients\nwith P4 below 1.5ng/ml;  p =0.004); a significantly bigger mean\nnumber of oocytes retrieved after OPU (14.7±11.3  vs. \n9.8±6.5 in the patients with P4 below 1.5ng/ml;\n p <0.001).\n\nPPO significantly reduces the quantity, but not the quality, of the oocytes available\nfor IVF treatment. Hence the cycles with PPO will have fewer available oocytes and,\nthus, fewer available embryos for transfer, but their quality will remain\nintact.\nTo our knowledge, this is the first study to analyze the impact of PPO on the\nquantity and quality of the whole oocyte cohort in IVF treatments. This phenomenon\nhas been previously addressed in the literature ( Craft  et al ., 1980 ;  Stanger & Yovich, 1984 ), and the competence of the oocytes retrieved\nfrom these prematurely ruptured follicles has already been proven ( Teramoto  et al ., 2019 ).\nHowever, the aim of the present study was to analyze the competence of the whole\nretrieved oocyte cohort to shed more light on what was already described by  Teramoto  et al . (2019) .\nPPO is not a very frequent phenomenon in IVF treatments (below 2% based on our data).\nNevertheless, our results may help with not only clinical decision making, but also\nclinicians to orientate and inform their patients about their chances with the IVF\ncycle once this phenomenon has been detected.\nGiven the low PPO frequency in our population, we performed the comparison of oocyte\nquantity and quality between the PPO IVF cycles and a control group of patients\nwithout PPO, but matched to the PPO group for age, BMI, treatment year, performed\nembryo genetic analysis and stimulation protocol type at a proportion of 1:3. This\ntype of analysis may avoid any bias regarding the huge sample size difference\nbetween the PPO and nonPPO groups. In contrast, and consequently, the main\nlimitation of this study is its small sample size.\nOur results clearly show a significant drop in both the recovery rate and the final\ntotal number of oocytes, mature oocytes, correctly fertilized oocytes and\ntop-quality blastocysts ( Table 2 ). Therefore,\nPPO significantly reduces oocyte quantity and, hence, the final number of usable\nblastocysts in that cycle. Indeed PPO reduces the recovery rate beyond the minimum\nthreshold taken in the literature as the optimal recovery rate, which is around\n75-85% of expected oocytes ( El-Shawarby  et\nal ., 2004 ;  Braga  et\nal ., 2020 ).\nIn contrast, these data suggest that PPO has no significant impact on oocyte quality,\nas shown by similar the maturation, fertilization and top-quality blastocyst rates\n( Table 2 ). The embryos from the PPO and\nnonPPO cycles have similar embryo quality rates according to the classification of\nthe Spanish Association for the Study of Reproduction Biology (ASEBIR) ( Table 3 ). Besides, the embryos from the PPO\ngroup went to the blastocyst stage at a similar ratio to the control embryos, which\nalso reinforces their similar quality ( Table\n3 ). So the fewer oocytes recovered after PPO have exactly the same\nquality as in the nonPPO cycles.\nFurthermore, PPO occurrence does not seem to affect pregnancy rates ( Table 3 ). More importantly, the mean number of\nET attempts until ongoing pregnancy or live birth was similar among groups ( Table 3 ). However, these comparisons in\npregnancy outcomes do not have enough statistical power (0.298 for biochemical\npregnancy, 0.166 for clinical pregnancy and 0.050 for ongoing pregnancy) to detect\nsignificant differences, which is probably due to the few ETs performed in both\ngroups, especially in the PPO group.\nHence if we clinicians detect PPO occurrence, but we think it is not worth canceling\nthe cycle despite fewer oocytes, we at least know that their quality will not be\nlost. Nevertheless, if they are implemented in routine clinical practice, the\nparameters for detecting PPO should be better defined to unify criteria.\nHowever, can we predict PPO occurrence in IVF treatments and, thus, act beforehand?\nOur results show that serum E2 and P4 levels on the triggering day, as well as the\ntype of trigger, could be potential markers of PPO ( Table 1 ). Cycles with PPO had significantly higher E2 and P4 levels on\nthe triggering day, and triggered with higher frequency using the GnRH agonist.\nAfter having adjusted for confounding factors, the three of them showed a\nsignificant correlation with PPO ( Table\n4 ).\nRegarding serum P4 levels ≥1.5ng/ml, which seem to exert the highest effect,\nit is true that a significantly higher proportion of PPO patients had P4 levels\nabove this cut-off point (28.8% in the PPO group  vs.  10.2% in the\ncontrol group;  p <0.001). Levels above this threshold point have\nbeen related to lower pregnancy rates in fresh ETs ( Bosch  et al ., 2010 ), which was, thus, the cut-off point\nused in this analysis.\nHowever, the proportion of patients with P4 levels exceeding this threshold on the\ntriggering day had significantly lower PPO (38.5% in the PPO group\n vs.  61.5% in the control group;  p <0.001).\nIn addition, P4 levels ≥1.5ng/ml were related to significantly more follicles\nin the last ultrasound prior to OPU (14.4±5.8  vs. \n11.6±5.4 in the group of patients with P4 below 1.5 ng/ml;\n p =0.004) and to significantly more retrieved oocytes\n(14.7±11.3  vs.  9.8±6.5 in the patients with P4 below\n1.5 ng/ml;  p =0.018). This scenario is completely the opposite of\nwhat our data suggest for the patients with PPO.\nHigh serum P4 levels on the triggering day might indicate the onset of premature\novulation risk and, hence, its correlation to PPO occurrence during OPU. Indeed it\nhas been suggested that an initial serum P4 rise in the late follicular phase might\nbe the physiological trigger of the ovulatory gonadotropins surge in humans prior to\nluteinizing hormone (LH) and estradiol peaks ( Dozortsev & Diamond, 2020 ). Nevertheless, our data cannot ensure PPO\noccurrence after having detected P4 levels above this cut-off point on the\ntriggering day.\nIn any event, main limitations of the present study include its retrospective design\nand its limited sample size, derived from the low occurrence of PPO in IVF\ntreatments. Thus, it is possible that potential differences in oocyte quality\ncouldn’t be detected due to the insufficient study power of this analysis. In\naddition, pregnancy outcomes cannot be firmly compared regarding the small number of\nembryo transfers included. Therefore, results from this study should be treated with\ncaution.\n\nPPO is a very uncommon phenomenon in controlled ovarian hyperstimulation IVF\ntreatments. Its occurrence significantly reduces the quantity, but not the quality,\nof the oocytes available for IVF treatment and, thus, still offers chances of\npregnancy. Serum P4 levels above the cut-off point of 1.5ng/mL on the triggering day\nmay suggest a higher risk of PPO, but its predictive value has not been confirmed.\nTherefore, cycle cancellation may not be worth associated losses of money, time and\nmorale once detected.","source_license":"CC-BY-4.0","license_restricted":false}