Natural Cycle Cryopreserved Embryo Transfer: is a Washout Period Needed after a Failure of Fresh Embryo Transfer?

Introduction: The optimal timing of frozen embryo transfer (FET) after a failed fresh IVF-ET cycle is controversial. Some studies support the postponement of FET for at least one menstrual cycle, while others suggest that such a "washout" period is unnecessary. Until now, published studies included only artificial FET cycles, and the use of the natural cycle has not been investigated.

Aim: To study whether delaying modified natural cycle (mNC) FET after a failed fresh ET affect pregnancy outcome.

Materials & Methods: We retrospectively reviewed all first FET cycles performed after failed fresh ET attempts between 2009 and 2016. Only mNC FET cycles were included, where hCG was used for ovulation triggering, and vaginal progesterone was given as luteal support. Cycles were divided according to the time interval between ovum pickup and FET into immediate group (

Results: A total of 212 cycles met the inclusion criteria, with 127 immediate FET and 85 delayed FET attempts. The study groups did not differ with regard to CPR (27.6% vs. 20.0%, respectively, p=0.21) or LBR (22.8% vs. 14.1%, respectively, p=0.11). On multivariate regression analysis, delaying mNC FET was not associated with CPR (aOR 0.61, 95%CI 0.30-1.24) or LBR (aOR 0.56, 95%CI 0.25-1.22), after controlling for woman’s age, infertility diagnosis, fresh ET protocol, and the number of embryos transferred.

Conclusion: In mNC FET cycles, delaying FET after a failed fresh cycle, does not improve the reproductive outcome. These data should reassure patients and clinicians who desire to proceed with FET immediately after fresh IVF failure.