A decrease in endometrial thickness before embryo transfer is not associated with preterm birth and placenta-mediated pregnancy complications

Research question: Does a decrease in endometrial thickness (compaction ≥10%) before embryo transfer prognosticate the risk for preterm birth and placenta-mediated pregnancy complications among IVF pregnancies?

Design: Retrospective cohort study at a large private fertility practice. Patients with a singleton live birth after a fresh or frozen embryo transfer between 2016 and 2019 were included. The primary outcome was preterm birth (delivery before 37 weeks gestational age). Secondary outcomes included gestational hypertension, pre-eclampsia, intrauterine growth restriction and placental abruption.

Results: Of the 252 patients that met the study criteria, 122 (48%) demonstrated endometrial compaction (≥10%) and 130 (52%) did not. Age, body mass index (BMI), parity, history of preterm birth or history of pre-existing maternal conditions between the compaction and no-compaction groups were not significantly different. The overall prevalence of placenta-mediated complications across all participants was 25% (n = 62). The number of preterm births between the compaction and no-compaction groups (13% and 6%, respectively, P = 0.09) as well as the prevalence of placenta-mediated complications (29.5% and 20%, respectively, P = 0.08) were not significantly different. Findings for the primary outcome (preterm birth) persisted even after adjustment for potential confounding variables, including maternal age, parity, BMI, embryo score and type of embryo transfer (fresh versus frozen) (adjusted OR 1.86, 95% CI 0.64 to 5.38).

Conclusions: Endometrial compaction (or decrease in endometrial thickness) before embryo transfer is not associated with preterm birth or placenta-mediated pregnancy complications.