Impact of single embryo transfer policy on perinatal outcomes in fresh and frozen cycles—analysis of the Japanese Assisted Reproduction Technology registry between 2007 and 2012

Objective To investigate whether the introduction of single embryo transfer (SET) policy in Japan has improved perinatal outcomes. Design A retrospective cohort study. Setting Not applicable. Patient(s) A total of 140,718 live births and 510 stillbirths (after 22 weeks of gestation) conceived by assisted reproductive technology in Japan between 2007 and 2012 were reviewed. Intervention(s) None. Main Outcome Measure(s) Preterm birth (PTB), low birth weight (LBW), very low birth weight (VLBW), small for gestational age (SGA), large for gestational age (LGA), perinatal mortality, and other pregnancy complications. Result(s) The rate of SET increased significantly from 52.2% in 2007 to 82.6% in 2012, while the rate of multiple pregnancy decreased significantly from 10.7% to 4.1% over the same period. The rates of PTB, LBW, and SGA decreased significantly, while that of LGA increased. Perinatal mortality decreased from 0.70% to 0.40% in fresh cycles, while that of frozen cycles did not change. Double ET or more was associated with a significantly increased risk for multiple pregnancy, placenta accreta, preterm premature rupture of membrane, cesarean section (CS), PTB, LBW, SGA, and early neonatal death compared with SET. Compared with before the SET policy was launched, the risks of multiple pregnancy, CS, early PTB before 32 weeks, LBW, VLBW, and SGA were significantly decreased after the policy was launched, with significant interactions of fresh/frozen status. Conclusion(s) The results suggest that the SET policy improved perinatal outcomes in Japan. The impact of SET policy was different in fresh and frozen cycles for several perinatal outcomes.