Endometrial thickness significantly affects clinical pregnancy and live birth rates in frozen-thawed embryo transfer cycles

Abstract

In order to explore the relationship between endometrial thickness on the day of embryo transfer and pregnancy outcomes in frozen-thawed embryo transfer (FET) cycles, we retrospectively analyzed data from 2997 patients undergoing their first FET cycles from January 2010 to December 2012. All patients were divided into three groups (Group A, ≤8 mm; Group B, 9–13 mm; Group C, ≥14 mm) according to the endometrial thickness on embryo transfer day. Compared with patients in the other two groups, patients with thin endometrial thickness in Group A had significantly lower clinical pregnancy rate (33.4%, 41.3% and 45.4%, p < 0.01) and live birth rate (23.8%, 32.2% and 34.0%, p < 0.01). After adjusting for age, body mass index (BMI), baseline follicle stimulating hormone (FSH) FET protocol and number of embryos transferred, the associations between medium endometrial thickness (Group B) and clinical pregnancy rate [adjusted odds ratio (aOR): 1.39; 95% confidence interval (CI): 1.10–1.77, p < 0.01] and live birth rate (aOR: 1.50; 95% CI: 1.16–1.95, p < 0.01) were significant. We conclude that for patients undergoing FET, endometrial thickness on the embryo transfer day significantly affects IVF outcomes in cleavage embryo transfer cycles independent of other factors.

Chinese abstract

为了研究胚胎冷冻-复苏移植（frozen-thawed embryo transfer, FET）周期中胚胎移植当日子宫内膜厚度与妊娠结局的相关性，我们回顾性分析了2010年1月至2012年12月接受首次FET周期的2997例患者的数据。所有患者依据胚胎移植当天的子宫内膜厚度被分为3组（组A，≤8 mm；组B，9–13 mm；组C，≥14 mm）。内膜厚度最薄的组A患者的临床妊娠率（33.4%，41.3%，45.4%，p < 0.01）与活产率（23.8%，32.2%，34.0%，p < 0.01）显著低于其他两组。在校准年龄、体重指数（BMI），基线卵泡刺激素（FSH）FET方案及胚胎移植数量后，中位子宫内膜厚度（组B）与临床妊娠率[校正比值比（aOR）：1.39；95%可信区间（CI）：1.10-1.77，p < 0.01]和活产率（aOR：1.50；95% CI：1.16-1.95，p < 0.01）存在显著相关性。研究表明，对于接受FET的患者，胚胎移植当天子宫内膜厚度可显著影响卵裂胚胎移植周期的IVF结局。

• Clinical pregnancy rate
• endometrial thickness
• frozen-thawed embryo transfer
• live birth rate

Acknowledgements

The authors would like to thank all the staff from Reproductive Medical Center, First Affiliated Hospital of Zhengzhou University.

Declaration of interest

There are no financial or commercial conflicts in this study. This work was supported by the National Natural Science Foundation of China (Grant NO.31271605).