The risk of placenta previa and cesarean section associated with a thin endometrial thickness: a retrospective study of 5251 singleton births during frozen embryo transfer in China.

PURPOSE: To determine whether the endometrial thickness (EMT) affects the occurrence of obstetric complications and neonatal outcomes in frozen embryo transfer (FET).

METHODS

We conducted a retrospective study that included singleton deliveries (N = 5251) resulting from FET in a single center between August 2013 and March 2016. Obstetric complications and neonatal outcomes were compared among patients with different EMTs, which were measured the day before embryo thawing. The women were divided into three groups based on the EMT: group 1: < 9 mm; group 2: 9-12 mm; group 3: > 12 mm. Multiple logistic regression and subgroup analyses were performed to determine the potential confounding factors.

RESULTS

The incidence of placenta previa in groups 1, 2, and 3 was 3.8, 1.0 and 0.5%, respectively, and that of cesarean section was 87.0, 78.3 and 72.0%, respectively (both P < 0.001). The gestational age and birth weight increased from group 1 to group 3 (both P < 0.001). After adjusting for confounders, a thicker EMT was found to be associated with a decreased risk of placenta previa (adjusted odds ratio (aOR) 0.798; 95% confidence interval (95% CI) 0.651-0.979; P = 0.031) and with a decreased risk of cesarean section (aOR 0.926; 95% CI 0.889-0.965; P < 0.001). Regarding the incidence of placenta previa, compared to women in group 3, women in group 1 had an aOR of 6.208 (95% CI 2.169-17.766; P = 0.001), and women in group 2 had an aOR of 1.862 (95% CI 0.851-4.076; P = 0.120). Regarding the incidence of cesarean section, compared to women in group 3, women in group 1 had an aOR of 2.111 (95% CI 1.415-3.455; P < 0.001), and women in group 2 had an aOR of 1.293 (95% CI 1.128-1.481; P < 0.001). Subgroup analyses showed similar results.

CONCLUSIONS

Our results demonstrate that a thin endometrial lining is associated with adverse obstetric and neonatal outcomes and might be related to poor placentation.