Endometrial thickness and IVF cycle outcomes: a meta-analysis

•Thin EMT induces lower pregnancy, implantation, live birth or ongoing pregnancy rates.•Thin EMT were not associated with the risk of abortion rate and ectopic pregnancy rate In this meta-analysis, the association between endometrial thickness (EMT) and cycle outcomes after IVF is explored. Associations between EMT and cycle outcomes according to study and individual characteristics were also assessed. Studies evaluating associations between EMT and pregnancy, implantation, miscarriage, live birth or ongoing pregnancy and ectopic pregnancy rates in individuals after IVF were identified on PubMed, Embase and the Cochrane Library (from their inception up to December 2018). Pooled odds ratios with 95% confidence intervals, calculated using the random-effects model, were used. Nine prospective and 21 retrospective studies, including a total of 88,056 cycles, were retrieved. The summary odds ratios indicated that women with lower EMT were associated with lower pregnancy rates than those with higher EMT (n = 30, OR 0.61; 95% CI 0.52 to 0.70; P < 0.001). Moreover, the implantation rate in women with lower EMT was significantly reduced (n = 9, OR 0.49; 95% CI 0.32 to 0.74; P = 0.001). Furthermore, no significant association was found between EMT and the miscarriage rate (n = 12). In addition, women with lower EMT were associated with reduced live birth or ongoing pregnancy rate (11 studies, OR 0.60; 95% CI 0.48 to 0.73; P < 0.001). Finally, the incidence of ectopic pregnancy rate between lower and higher EMT showed no statistically significant association (n = 3). Lower EMT was associated with lower pregnancy, implantation and live birth or ongoing pregnancy rates.