Quality or quantity? Pitfalls of assessing the effect of endometrial thickness on live birth rates

Abstract

The study by Mahutte et al. ( 1 Mahutte N. Hartman M. Meng L. Lanes A. Luo Z.C. Liu K.E. Optimal endometrial thickness in fresh and frozen-thaw in vitro fertilization cycles: an analysis of live birth rates from 96,000 autologous embryo transfers. Fertil Steril. 2022; 117: 792-800 Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar ) to identify “an optimal endometrial thickness” for embryo transfer has some limitations that could have led to inaccuracies. Although they reported that endometrial thickness was negatively correlated with patient age and positively correlated with parity, peak estradiol levels, numbers of oocytes at retrieval, and embryos available for transfer or cryopreservation in their dataset, none of their analyses were simultaneously adjusted for these confounding factors that also affect the live birth rate ( 1 Mahutte N. Hartman M. Meng L. Lanes A. Luo Z.C. Liu K.E. Optimal endometrial thickness in fresh and frozen-thaw in vitro fertilization cycles: an analysis of live birth rates from 96,000 autologous embryo transfers. Fertil Steril. 2022; 117: 792-800 Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar ). Even the number of embryos transferred, which was significantly different between categories of endometrial thickness in fresh transfers, was not adjusted for (Supplemental Table 1 [available online] by Mahutte et al.) ( 1 Mahutte N. Hartman M. Meng L. Lanes A. Luo Z.C. Liu K.E. Optimal endometrial thickness in fresh and frozen-thaw in vitro fertilization cycles: an analysis of live birth rates from 96,000 autologous embryo transfers. Fertil Steril. 2022; 117: 792-800 Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar ). Simultaneous adjustment for multiple confounders in a single model may have yielded different results, for example, the “surprising” relationship between thicker endometrial linings and live birth rates in fresh transfers may not have been observed ( 1 Mahutte N. Hartman M. Meng L. Lanes A. Luo Z.C. Liu K.E. Optimal endometrial thickness in fresh and frozen-thaw in vitro fertilization cycles: an analysis of live birth rates from 96,000 autologous embryo transfers. Fertil Steril. 2022; 117: 792-800 Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar ). Optimal endometrial thickness in fresh and frozen-thaw in vitro fertilization cycles: an analysis of live birth rates from 96,000 autologous embryo transfersFertility and SterilityVol. 117Issue 4PreviewTo study the effect of increasing endometrial thickness on live birth rates in fresh and frozen-thaw embryo transfer (FET) cycles. Full-Text PDF Open AccessReply of the Authors: Quality or quantity? Pitfalls of assessing the effect of endometrial thickness on live birth ratesFertility and SterilityVol. 118Issue 2PreviewThe investigators thank Ata et al. for their comments on our study. Although we chose to use stratification to account for potential confounders in our manuscript (1), we agree that multivariate regression is another method that could be used. We have run an unadjusted modified Poisson regression for the live birth rate for both fresh embryo transfers and frozen embryo transfers (FETs), and the findings are consistent with the results reported in our manuscript. The exposure groups for these models were categorized according to the endometrial thickness: <7.0; 7.0–7.9 (reference group); and ≥8.0 mm. Full-Text PDF