Outcome variables assessed
Live birth was defined as the delivery of at least one live-born baby at greater than 24 weeks of gestational age. Clinical pregnancy was defined as the presence of at least one viable fetal cardiac activity at the 6-8 weeks transvaginal ultrasound. Miscarriage was defined as a 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.