Effect of the endometrial thickness on the live birth rate: insights from 959 single euploid frozen embryo transfers without a cutoff for thickness.

Objective: To investigate whether endometrial thickness (ET) independently affects the live birth rate (LBR) after embryo transfer.

Design: Retrospective study.

Setting: Private assisted reproductive technology center.

Patient(s): A total of 959 single euploid frozen embryo transfers.

Intervention(s): Vitrified euploid blastocyst transfer.

Main Outcome Measure(s): Live birth rate per embryo transfer.

Result(s): The conditional density plots did not demonstrate either a linear relationship between the ET and LBR or a threshold below which the LBR decreased perceivably. Receiver operating characteristic curve analyses did not suggest a predictive value of the ET for the LBR. The area under the curve values were 0.55, 0.54, and 0.54 in the overall, programmed, and natural cycle transfers, respectively. Logistic regression analyses with age, embryo quality, day of trophectoderm biopsy, body mass index, and ET did not suggest an independent effect of the ET on the LBR.

Conclusion(s): We did not identify a threshold of the ET that either precluded live birth or under which the LBR decreases perceivably. Common practice of cancelling embryo transfers when the ET is <7 mm may not be justified. Prospective studies, in which the management of the transfer cycle would not be altered by ET, would provide higher-quality evidence on the subject.