Definition of pregnancy
A serum β-hCG assay 11-14 days after ET. Clinical pregnancy was defined
as the presence of a gestational sac on transvaginal ultrasound.
Clinical miscarriage was defined if the pregnancy terminated before 12
weeks of gestational age. Implantation rate was defined as the number of
intrauterine sacs divided by the number of embryos transferred.
Ongoing pregnancy was defined as gestations that reached 20 weeks or
more. Live birth was defined as give birth to an infant ≥24 weeks’
gestation.