18A - A Natural Cycle Is the Best Protocol for Frozen Embryo Replacement

Summary

The choice of protocol for FET cycle depends on the individual woman’s ovarian function and convenience of the method, as well as on the experience gained with the method by the physicians. It appears, that in ovulatory women, endometrial preparation for FET which includes NC-FET, with or without modified/luteal support, results in the highest pregnancy and live-birth rates, both in the general IVF population and also in those undergoing euploid blastocyst transfer, as compared to AC- FET. It is also well known that FET is associated with lower risk of prematurity, small for gestational age, and low birth weight and increased risk of large for gestational and/or macrosomic in singletons, when compared with fresh ET. Moreover, the relative risk of hypertensive disorders in pregnancy, as well as perinatal mortality were also demonstrated to be increased in FET compared with singletons from fresh ET and natural conception. Recent studies have related the aforementioned pregnancy complications to the endometrial priming and not to the cryopreservation process, with higher risk in programmed FET rather than those following natural cycles. Thus, when considering elective freeze-all policy in ovulatory patients, FET following natural cycle is advised aiming to increase LBR and reduce adverse outcomes.