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;