Does the time interval between oocyte retrieval and frozen embryo transfer (FET) affect pregnancy outcomes after a freeze-all strategy?
In a retrospective study, a total of 5995 patients who underwent their first FET following a freeze-all cycle between January 1, 2017, and December 31, 2020, were included. Patients were divided into immediate (the interval between oocyte retrieval and the day of first FET was ≤40 days), delayed (>40 days but ≤180 days) and overdue groups (>180 days). Pregnancy and neonatal outcomes were analyzed, and multivariable regression analysis was used to study the effect of FET timing on the live birth rate (LBR) in the entire cohort and the different subgroups.
The LBR was significantly lower in the overdue group than in the delayed group (34.9% vs. 42.8%, P=0.002); however, after adjusting for confounding factors, the difference was not statistically significant. The immediate group had a comparable LBR (36.9%) with the other two groups in both the crude and adjusted analyses. Multivariable regression analysis showed no impact of FET timing on LBR in the whole cohort or in the subgroups according to controlled ovarian hyperstimulation protocol, trigger type, insemination method, reason for freezing all, FET protocol, and transferred embryo stage.
The time interval between oocyte retrieval and FET does not impact reproductive outcomes. Unnecessary delays in FET should be avoided to shorten the time to live birth.
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Ying Wang, MD, PhD, Chief Physician at the Department of Obstetrics and Gynecology at Peking University Third Hospital. A member of the American Society of Reproductive Medicine, the European Society of Human Embryology and Reproduction, and the Chinese Eugenics Science Association. She hosted and participated several National Natural Science foundations.
Accepted: March 6, 2023
Received in revised form: March 4, 2023
Received: December 16, 2022
Publication stageIn Press Journal Pre-Proof
© 2023 Published by Elsevier Ltd on behalf of Reproductive Healthcare Ltd.