Supraphysiological estradiol level in ovarian stimulation cycles affects the birthweight of neonates conceived through subsequent frozen-thawed cycles: a retrospective study.

Objective: To investigate whether supraphysiological estradiol (E2 ) in controlled ovarian stimulation (COS) cycles affects the subsequent frozen-thawed embryo transfer (FET) in terms of the neonatal birthweight.

Methods: Retrospective cohort study. Methods: University affiliated hospital. Methods: In all, 2066 patients undergoing FET cycles that resulted in live singleton births between July 2011 and Dec 2016. Methods: None. Methods: Multivariable linear regression and logistic regression was used to evaluate the association between peak E2 and birthweight outcomes. Methods: Birthweight, z-score adjusted for gender and gestational age, and incidence of small-for-gestational-age (SGA) and low birthweight (LBW) in singleton neonates derived from FET cycles.

Results: Adjusted for confounding factors, both the absolute birthweight and the z-score of singletons following FET were negatively associated with peak E2 levels in COS. In comparison with the referent category (E2  ≤1500 pg/ml), the categories with E2  >3000 pg/ml had a significantly lower z-score. The difference (95% CI) in estimated marginal mean of birthweights between referent category and highest E2 (>8000 pg/ml) category was 104.57 g (18.13-181.06). Multiple logistic regression analyses showed that the adjusted odds ratio (95% CI) for SGA and LBW in term singletons comparing patients with E2  >3000 pg/ml with those with E2  ≤3000 pg/ml was 2.44 (1.37-4.34) and 2.32 (1.01-5.40), respectively.

Conclusions: Peak E2 levels in COS cycles are negatively associated with the birthweight of singletons conceived through subsequent FET cycles. Conclusions: The birthweight following FET is affected by previous COS cycle.