Does high serum oestradiol during stimulation influence obstetrical outcomes and placental pathology in subsequent frozen embryo transfers?

AIM: High oestradiol levels during in vitro fertilization (IVF) fresh cycles have been linked to adverse obstetric outcomes, yet whether this is due to endometrial or oocyte effects remains unclear. Investigating subsequent frozen embryo transfer (FET) cycles can help clarify the origins of these effects. This study aimed to evaluate obstetric outcomes and placental histology in FET cycles for patients with elevated serum oestradiol levels during the ovarian stimulation cycle in which the embryos were created. METHODS: A single centre retrospective cohort study of live singleton deliveries after IVF with programmed FET from 2009 to 2017. High oestradiol during ovarian stimulation was defined as ≥10,000 pmol/L. We compared obstetric outcomes and placental findings between pregnancies with high oestradiol levels in the preceding ovarian stimulation cycle and a control group. RESULTS: We analyzed 114 deliveries in the high oestradiol group and 194 in the control group. Baseline demographics were comparable between groups. No significant differences were observed in obstetric outcomes, including low birth weight, preeclampsia and preterm delivery. The placental macroscopic and histopathological findings did not significantly differ between the groups as well. CONCLUSION: High oestradiol during the ovarian stimulation cycle used to create embryos is not associated with adverse obstetric outcomes or placental pathologies in pregnancies following FET. This is consistent with an endometrial effect of high oestradiol and thus support the practice of a freeze all approach in high oestradiol cycles.