Pregnancy-related complications and perinatal outcomes resulting from transfer of cryopreserved versus fresh embryos in vitro fertilization: a meta-analysis

Objective: To provide an updated comparison of pregnancy-related complications and adverse perinatal outcomes of pregnancies conceived after frozen embryo transfer (FET) versus fresh embryo transfer (fresh ET). Design: Meta-analysis. Setting: University. Patient(s): Pregnancies resulting from FET versus fresh ET. Interventions(s): Pubmed, Embase, Cochrane Library, Google Scholar, and Chinese databases, including the China National Knowledge Infrastructure Database, Wanfang, and Chinese Scientific Journals Full-Text Database were searched by two independent reviewers from January 1980 to September 2017. The results were expressed as risk ratios with 95% confidence intervals. Main Outcome Measure(s): Pregnancy-related complications and perinatal outcomes. Result(s): Our search retrieved 1,397 articles, of which 31 studies were included. Pregnancies resulting from FET were associated with lower relative risks of placenta previa, placental abruption, low birth weight, very low birth weight, very preterm birth, small for gestational age, and perinatal mortality compared with fresh ET. Pregnancies occurring from FET were associated with increased risks of pregnancy-induced hypertension, postpartum hemorrhage, and large for gestational age compared with fresh ET. The risks of gestational diabetes mellitus, preterm premature rupture of the membranes, and preterm birth (PTB) showed no differences between the two groups. Conclusion(s): Our analysis demonstrated that FET results in lower risks of placenta previa, placental abruption, low birth weight, very low birth weight, very preterm birth, small for gestational age, and perinatal mortality than fresh ET, some differences that are attributed to the increased risks of pregnancy-induced hypertension, large for gestational age, and postpartum hemorrhage. Although cryotechnology keeps improving, for comprehensive consideration, individual approaches remain appropriate to balance the options of FET or fresh ET at present. (C) 2017 by American Society for Reproductive Medicine.