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

OBJECTIVES: To 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. DESIGN: We performed a secondary analysis of a retrospective cohort study of deliveries linked to in vitro fertilization (IVF) cycles. SETTING: Deliveries were performed over fifteen years at a single tertiary hospital. All IVF cycles were performed at a single infertility treatment center. PATIENTS: 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: We compared pregnancies resulting from frozen embryo transfer (frozen) cycles to those resulting from fresh embryo transfer (fresh) cycles. MAIN OUTCOME MEASURES: The primary outcome was a composite outcome of IPD or IUFD due to placental insufficiency. IPD included preeclampsia, placental abruption, and small for gestational age (SGA). We calculated risk ratios (RR) and 95% confidence intervals (CI). RESULTS: Compared to 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 preeclampsia (RR 1.3, 95% CI: 0.84-1.9) and abruption (RR 1.2, 95% CI: 0.56-2.4) were similar. CONCLUSION: There was a lower risk of IPD among frozen cycles compared to fresh cycles. This association was largely driven by lower risk of SGA among frozen cycles.