Predictive Value of Decreased Serum Estradiol Levels Following Human Chorionic Gonadotropin Trigger For Unexpected Ovulation During In Vitro Fertilization Cycle of Patients With Poor Ovarian Response

Background Unexpected spontaneous ovulation typically occurs in patients with poor ovarian response (POR); however, reliable predictors are lacking. We analyzed explore the predictive value of decreased serum estradiol (E2) levels on the day after human chorionic gonadotropin (hCG) trigger during in vitro fertilization (IVF) cycles. Methods We retrospectively analyzed clinical data (n = 978) in IVF cycles between 2017 and 2020. According to decreased ratios of E2 levels (△E2%) between day 1 and day 0 of hCG trigger, patients were divided into: ≤10% (group A), 10–20% (group B), and ≥ 20% (group C). Basic characteristics and laboratory data were compared using analysis of variance or Mann–Whitney U-test. Logistic regression and receiver operating characteristic (ROC) curve analyses were used to assess the relationship between △E2% and spontaneous unexpected ovulation. Fresh embryo transfer cycles in groups A, B, and C were subgrouped as A1, B1, and C1, respectively; clinical outcomes were compared. Results Mean E2 and luteinizing hormone (LH) levels, ratio of premature LH peak and high progesterone levels, time interval between hCG trigger and oocyte retrieval, number of follicles ≥ 11 mm in diameter, and dose regimen of gonadotropin among the three groups showed significant differences (P < 0.05). After adjusting for relevant confounders, likelihood ratios of unexpected ovulation in groups B and C were 2.96 (95 % confidence interval [CI]: 0.64–13.70), and 11.74 (95 % CI: 3.09–44.62), respectively, compared with that in group A. The test for trend was significant before and after correction (P for trend < 0.05). On combining premature LH peak (> 10 mIU/mL) or high progesterone level (> 1.0 ng/mL) on the day of hCG, area under ROC curve (AUC) was 0.849 (95 % CI, 0.764–0.934, P < 0.05). However, when we only considered △E2%, AUC was 0.738 (95 % CI. 0.562–0.914, P < 0.05). Rates of embryo implantation, clinical pregnancy, live birth in fresh embryo transfer cycle, and early abortion among the three subgroups did not differ significantly (P > 0.05). Conclusions E2 levels on the day after hCG trigger are valuable for predicting unexpected ovulation. However, their decreased levels do not directly affect clinical pregnancy outcomes.