Adverse obstetric and perinatal outcomes in 1,136 singleton pregnancies conceived after programmed frozen embryo transfer (FET) compared with natural cycle FET

To investigate whether obstetric and perinatal outcomes in pregnancies differ after different frozen embryo transfer (FET) protocols. Register-based cohort study. Not applicable. All singleton deliveries after assisted reproductive technology in Denmark from 2006 to 2014. Data consisted of 1,136 deliveries after frozen in vitro fertilization. Frozen embryo transfer cycles were grouped by type of FET protocol: programmed FET (n = 357); modified natural cycle FET (n = 611); and true natural cycle FET (n = 168). None. Obstetric outcomes (hypertensive disorders in pregnancy, preterm prelabor rupture of membranes, placenta previa, placental abruption, induction of labor, postpartum hemorrhage, and cesarean section) and perinatal outcomes (post-term birth, preterm birth, birth weight, small for gestational age, large for gestational age). The risk of hypertensive disorders in pregnancy, postpartum hemorrhage, and cesarean section was significantly higher after programmed FET compared with natural cycle FET (modified natural cycle FET and true natural cycle FET). A higher risk of birth weight > 4,500 g was observed in the programmed FET group compared with natural cycle FET. This study shows that obstetric and perinatal outcomes are adversely affected in programmed FET cycles. Hence, when possible, an endometrial preparation with the creation of a corpus luteum should be considered. Properly sized randomized controlled trials of FET in programmed cycle versus natural cycle including perinatal outcomes are warranted in the future. ISRCTN11780826. Resultados obstétricos y perinatales adversos en 1.136 embarazos únicos concebidos tras programar la transferencia del embrión congelado (FET) en ciclo sustituido comparado con FET en ciclo natural. Evaluar si los resultados obstétricos y perinatales de los embarazos difieren tras aplicar distintos protocolos para transferencia de embriones criopreservados (FET). Estudio de cohortes basado en un registro. No aplicable. Todos los partos de embarazo único tras técnicas de reproducción asistida en Dinamarca entre 2006 y 2014. Los datos consistieron en 1.136 partos tras fecundación in vitro con tránsfer de congelados. Los ciclos de FET se agruparon por tipo de protocolo: FET programado/sustituido (n = 357), FET en ciclo natural modificado (n = 611) y FET en ciclo natural real (n = 168). Ninguna. Resultados obstétricos (enfermedad hipertensiva en el embarazo, rotura prematura de membranas pretérmino antes del inicio del trabaj