Obstetric outcome in singletons after in vitro fertilization with cryopreserved/thawed embryos.

BACKGROUND There is increasing use of cryopreservation in IVF. This study compared singletons born after cryopreservation with singletons born after fresh IVF cycles and singletons born to women in the general population. METHODS Data were collected for Swedish IVF treatments during the years 2002-2006. All singletons from single embryo transfer (SET) and double embryo transfer (DET) after cryopreserved (n = 2348) and fresh cycles (n = 8944) were included and cross-linked with the Swedish Medical Birth Registry and compared with all singletons born after spontaneous conception (n = 571 914). Main outcomes were preterm and very preterm birth and low and very low birthweight (VLBW). Other outcomes were small for gestational age, large for gestational age (LGA), perinatal mortality and maternal outcomes. RESULTS Singletons from cryopreserved SET/DET or cryopreserved SET had increased rates of extreme preterm birth compared with singletons from the general population. A lower rate of LBW was found for cryopreserved SET/DET singletons compared with singletons from fresh cycles; however, a higher rate of perinatal mortality was detected. The rates of LGA and macrosomia were increased for cryopreserved SET/DET singletons when compared with those from fresh cycles and the general population. For maternal outcomes, a higher rate of pre-eclampsia was noted for pregnancies from cryopreserved cycles compared with those from fresh cycles or the general population, but the rate of placenta praevia was lower in pregnancies from cryopreserved cycles compared with those from fresh cycles. CONCLUSIONS The obstetric outcome of singletons after cryopreservation was slightly poorer when compared with the general population. In comparison with fresh cycles, the outcome varied. The finding of an increased rate of LGA after cryopreservation requires further study.