Thicker endometrial linings are associated with better IVF outcomes: a cohort of 6331 women

Our objective was to determine if a correlation exists between endometrial thickness measured on the day of ovulation trigger during an in vitro fertilization (IVF) cycle and pregnancy outcomes among non-cancelled cycles. We performed a retrospective cohort study looking at 6331 women undergoing their first, fresh autologous IVF cycle from 1 May 2004 to 31 December 2012 at Boston IVF (Waltham, MA). Our primary outcome was the risk ratio (RR) of live birth and positive β-hCG. We found that thicker endometrial linings were associated with positive β-hCG and live birth rates. For each additional millimetre of endometrial thickness, we found a statistically significant increased risk of positive β-hCG (adjusted RR: 1.14; 95% CI: 1.09-1.18) and live birth (RR: 1.08; 95% CI: 1.05-1.11). There was no association between endometrial thickness and miscarriage (RR: 0.99; 95% CI: 0.91-1.07). Similar results were seen when categorizing endometrial thickness. Compared with an endometrial thickness >7 to <11 mm, the likelihood of a live birth was significantly higher for an endometrial thickness ≥11 mm (adjusted RR: 1.23; 95% CI: 1.11-1.37) and significantly lower for the ≤7 mm group (adjusted RR: 0.64; 95% CI: 0.45-0.90). In conclusion, thicker endometrial linings were associated with increased pregnancy and live birth rates.