Outcome measures
According to ASRM consensus and ACOG, the definition of clinical outcomes was confirmed9,10. Our main outcome was live birth while miscarriage rate, clinical pregnancy rate, preterm birth rate, and ectopic pregnancy rate were secondary outcomes. Live birth was defined as the delivery of at least one live-born baby beyond 22 weeks of gestation. Live birth rate was defined as live deliveries (at least one live birth) per woman after embryo transfer. Miscarriage rate was defined as the spontaneous loss of a clinical pregnancy before 22 completed weeks of gestational age per clinical pregnancy cycle. Clinical pregnancy was defined as a pregnancy diagnosed by ultrasonographic visualization of one or more gestational sacs or definitive clinical signs of pregnancy. Preterm birth was defined as a birth that takes place after 22 weeks and before 37 completed weeks of gestational age. Ectopic pregnancy was defined as gestational sac observed by ultrasound outside the uterine cavity. Implantation rate was defined as the number of gestational sacs observed divided by the number of embryos transferred.