Neonatal and maternal outcome after frozen embryo transfer: Increased risks in programmed cycles

Abstract

Background Frozen embryo transfer is associated with better perinatal outcome regarding preterm birth and low birthweight, yet higher risk of large for gestational age and macrosomia compared to fresh transfer. Further, higher rates of hypertensive disorders in pregnancy are noted after frozen embryo transfer. Whether these differences are due to the protocol used in frozen cycles remains unknown. Objective To analyze the obstetric outcome after frozen embryo transfer depending on protocol used. Comparison was also made for frozen vs fresh transfer and for frozen transfer vs spontaneous conception. Study design A population-based retrospective registry study including all singletons born after frozen embryo transfer in Sweden from 2005 to 2015. The in vitro fertilization register was cross-linked with the Medical Birth Register, the Register of Birth Defects, the National Patient Register, the Swedish Neonatal Quality Register, and the Prescribed Drug Register. Singletons after frozen embryo transfer were compared depending on the presence of a corpus luteum in the actual cycle. All frozen transfer singletons were also compared with fresh transfer and spontaneous conception singletons. Primary outcomes were preterm birth ( 1000 mL). Crude and adjusted odds ratio with 95% confidence interval were calculated and adjustment made for relevant confounders. Results A total of 9726 singletons were born after frozen embryo transfer (natural cycles, n = 6297; stimulated cycles, n = 19…