Pereira N, et al. - A retrospective cohort study is done to investigate the effect of estradiol (E₂) levels on pregnancy and perinatal outcomes in programme frozen-thawed embryo transfer (FET) cycles. The outcomes of the current study propose that the hyperestrogenic milieu in programmed FET cycles may adversely affect pregnancy and perinatal outcomes, though to a lesser extent than fresh IVF. Careful monitoring of peak E₂ levels may be prudent even in programmed FET cycles.