Is There A Critical Endometrial Lining Thickness For Successful Implantation In A Programmed Cycle?.

The relationship of endometrial thickness to implantation rates has been debated since 1989 1,2. Some studies have suggested a specific cutoff of 7- 8 mm or greater correlates with a statistically significant improvement in pregnancy rates 3,4 5. A meta-analysis including only fresh cycles concluded that current data indicates that endometrial thickness has a limited capacity to predict implantation rates6. Programmed cycles with a different hormonal milieu than fresh cycles might offer a different implantation potential. This study was undertaken to determine the optimal endometrial thickness in a programmed cycle. An IRB approved retrospective cohort study from a single private IVF center. 909 autologous first frozen embryo transfer cycles with a single euploid embryo (euSFET) were analyzed from January 2014 to February 2020. The first objective was to determine if euSFET removes the age-related decline in sustained implantation rate (SIR) defined as ongoing pregnancy rate >20 weeks gestation. SIRs were compared between SART age groups (< 35, 35-37, 38-40, and > 41) using a Chi-Square test or a Fisher’s exact test, if assumptions were not met. Logistic regression was used to determine the odds ratios for SIR between endometrial thickness and SIR. Endometrial thickness was divided into the following groups: < 7mm, 7-8mm, 9-12mm, and > 12mm. A receiver operating curve (ROC) was created to identify the optimal endometrial thickness for implantation. The effect of age on SIR with euSFET was not found to be significant at any level: 60% < 35 group (n=361), 60% in 35-37 group (n=220), 56% in 38-40 group (n=223), and 55% in >41 group (n=105), respectively. Increasing endometrial thickness appears to have a positive effect on SIR: 46.67%, < 7mm (n=30), 51.5%, 7-8mm (n=266), 62.02% 9-12mm (n=445), and 63.9% > 12mm (n=168). Odds of implantation were 1.21 (95%CI: (.57, 2.59)) times higher in the 7-8mm group, 1.87 (95%CI: (.89, 3.92)) times higher in the 9-12mm group, and 2.00 (95%CI: (.92, 4.39)) times higher in the > 12mm group. Endometrial thickness over 12mm demonstrated a marked improvement in SIR (p =.08). ROC shows 8.35 mm to be the optimal thickness for a successful SIR. This data demonstrates that endometrial thickness has a positive effect on SIR in euSFET in programmed cycles. Carefully controlled trials are needed to further demonstrate the effect of endometrial thickness on SIR.Tabled 1Table 1Effect of age on SIRAge groupNSIRP< 3536160%0.8435-3722060%0.8538-4022356%0.33> 4110555%0.37Effect of endometrial thickness on SIRET groupNSIRPOR (95% CI)< 7 mm3046.40%0.72.88 (.43, 1.79)7-8mm26651.50%0.621.21 (.57, 2.59)9-12mm44562.02%0.11.87 (.89, 3.92)> 12mm16863.90%0.082.00 (.92, 4.39) Open table in a new tab