Risk of ischemic placental disease in fresh and frozen embryo transfer cycles.

ObjectivesTo evaluate the association of fresh and frozen embryo transfer with the development of ischemic placental disease (IPD), hypothesizing that differences in implantation environment affect placentation and thus pregnancy outcomes.DesignWe performed a secondary analysis of a retrospective cohort study of deliveries linked to IVF cycles.SettingTertiary hospital and infertility treatment center.Patient(s)We included all women who underwent an autologous IVF cycle and had a live-born infant or an intrauterine fetal demise (IUFD). We excluded women less than 18 years of age.Intervention(s)We compared pregnancies resulting from frozen embryo transfer (frozen) cycles with those resulting from fresh embryo transfer (fresh) cycles.Main outcome measure(s)The primary outcome was a composite outcome of IPD or IUFD due to placental insufficiency. Ischemic placental disease included pre-eclampsia, placental abruption, and small for gestational age (SGA). We calculated risk ratios (RRs) and 95% confidence intervals (CIs).Result(s)Compared with fresh cycles, frozen cycles had a lower risk of IPD or IUFD from placental insufficiency (RR 0.75, 95% CI 0.59-0.97). Frozen cycles also conferred a lower risk of SGA than fresh cycles (RR 0.58, 95% CI 0.41-0.81). Risks of pre-eclampsia (RR 1.3, 95% CI 0.84-1.9) and abruption (RR 1.2, 95% CI 0.56-2.4) were similar.Conclusion(s)There was a lower risk of IPD among frozen cycles compared with fresh cycles. This association was largely driven by lower risk of SGA among frozen cycles.