Impact of frozen-thawed single-blastocyst transfer on maternal and neonatal outcome: an analysis of 277,042 single-embryo transfer cycles from 2008 to 2010 in Japan.

OBJECTIVE: To evaluate the relationship between frozen-thawed single blastocyst transfer (BT) and maternal and neonatal outcomes of pregnancy.

DESIGN: Retrospective analysis.

SETTING: Japanese nationwide registry of assisted reproductive technology (ART) with mandatory reporting for all ART clinics in Japan.

PATIENT(S): Registered from 2008 through 2010 undergoing single embryo transfer cycles (n = 277,042).

INTERVENTION(S): None.

MAIN OUTCOME MEASURE(S): Rates of preterm birth (PTB; <37 weeks' gestation), low birth weight (LBW; <2,500 g), small for gestational age (SGA), large for gestational age (LGA), placenta previa, placenta abruption, placenta accreta, and pregnancy-induced hypertension (PIH) after fresh/frozen-thawed and cleaved-embryo/blastocyst transfers were performed.

RESULT(S): Frozen-thawed embryo transfer (FET) was associated with a significantly reduced occurrence of PTB, LBW, and SGA but increased rate of LGA. FET was also associated with a higher incidence of placenta accreta (odds ratio 3.16) and PIH (odds ratio 1.58). BT was associated with a significantly decreased rate of SGA and increased rate of LGA. There was no significant association between BT and maternal complications.

CONCLUSION(S): Frozen-thawed BT is associated with improved general perinatal outcomes of pregnancy but significantly increased maternal risks of placenta accreta and PIH. This finding requires further investigation to assure maternal safety of patients undergoing ART treatment.