Natural Versus Programmed Frozen Embryo Transfer (NatPro)

NatPro is a two-arm, parallel-group, multi-center, randomized trial in which women undergoing FET will be randomized to receive either a modified natural cycle (corpus luteum present) or a programmed cycle (corpus luteum absent). The study will implement a stratified randomization design to balance the use of pre-implantation genetic testing (PGT) across the two treatment arms. Each participant will have up to 3 FET cycles until live birth occurs, or the participant has no embryos available for transfer. Primary endpoints will be the proportion of women experiencing preeclampsia comparing modified natural to programmed FET among women with viable pregnancy (defined as pregnancy lasting at least 20 weeks) and the cumulative proportion of women having live births in the two arms.