Received March 01, 2026
Accepted March 09, 2026

Frozen embryo transfer (FET) has gained widespread popularity over the past decade, largely due to advancements in vitrification techniques. To optimize pregnancy rates in FET cycles, accurate synchronization between embryo development and endometrial receptivity is essential. However, the ideal, individualized approach to endometrial preparation remains a matter of ongoing debate. This review summarizes the current literature on endometrial preparation protocols and their impact on pregnancy and perinatal outcomes, with particular focus on artificial, natural, and stimulated cycles. While many studies are of limited methodological quality, some well-designed randomized controlled trials suggest improved pregnancy rates and better perinatal outcomes in FET compared to fresh embryo transfer, including a lower risk of preterm delivery and ovarian hyperstimulation syndrome (OHSS). Nonetheless, artificial endometrial preparation—characterized by the absence of a corpus luteum—has been associated with a higher incidence of hypertensive disorders of pregnancy and large-for-gestational-age (LGA) infants. This has reignited interest in whether transferring frozen embryos into a more “physiological” endometrium, as seen in natural or modified natural cycles, may not only enhance implantation but also reduce maternal and neonatal morbidity. The emergence of personalized luteal phase support across different protocols is another promising area that warrants further investigation. This narrative review provides a comprehensive overview of endometrial preparation strategies for FET and their effects on clinical outcomes, based on the latest available evidence.