Definition of clinical outcomes
Clinical pregnancy was defined as the presence of gestational sac at the 6-8 weeks transvaginal ultrasound. Ectopic pregnancy was defined as gestational sac observed by ultrasound outside the uterine cavity. Miscarriage was defined as spontaneous loss of a clinical pregnancy before 24 completed weeks of gestational age, in which the embryo(s) or fetus(es) is/are nonviable and is/are not spontaneously absorbed or expelled from the uterus. Preterm birth was defined as a birth that takes place after 24 weeks and before 37 completed weeks of gestational age. Live birth was defined as the delivery of at least one live-born baby beyond 24 weeks of gestational age. Live birth rate was defined as live deliveries (at least one live birth) per women after embryo transfer.