Which is better for mothers and babies, fresh or frozen thawed blastocyst transfer?
Abstract Background: In recent years, there have been emerging many reports on the pregnancy outcomes of fresh blastocyst transfer (BT) and freeze-thaw BT, but these couclusions are controversial and incomplete. To compare the pregnancy outcomes, maternal complications and neonatal outcomes of fresh and frozen-thawed BT in vitro fertilization or intracytoplasmic sperm injection (IVF/ICSI) cycles, we conducted a meta-analysis. Methods: A meta-analysis was conducted by searching PubMed, Embase, and Cochrane Library until January 2020. Data were extracted independently by two authors. Results: 42 studies, including 12 randomized controlled trials (RCT) met the inclusion criteria. Fresh BT showed lower implantation rate (IR), pregnancy rate (PR), ongoing pregnancy rate (OPR) and higher eptopic pregnancy rate (EPR) compared with frozen-thawed BT consistent with the results of RCT. The risks of moderate or severe ovarian hyperstimulation syndrome (OHSS), placental abruption (PA) and preterm were higher in fresh BT than in the frozen-thawed BT. The risk of pregnancy-induced hypertension (PIH) and pre-eclampsia was decreased in fresh BT , however, no significant differences of risks for PIH, pre-eclampsia, OHSS, and preterm was found between the two group in the 2 RCT included. Compared with frozen-thawed BT, fresh BT appears to be associated with small for gestational age (SGA) and low birth weight (LBW). No differences in the incidences of neonatal mortality and neonatal malformations were observed between fresh and frozen-thawed BT. Conclusions: In summary, Considering the higher IR, PR, OPR, lower EPR, and the decreased risks of OHSS, PA and preterm, as well as the incidences of SGA and LBW in frozen-thawed BT, this meta-analysis indicates that frozen-thawed BT may be a better choice for mothers and babies compared with fresh BT. Key words: Fresh blastocyst transfer, frozen thawed blastocyst transfer, pregnancy outcome, maternal complications, neonatal outcomes