Pregnancy outcomes
The primary pregnancy outcome was the cumulative live birth (CLB),
defined as at least one liveborn baby at ≥ 20 weeks gestation resulting
from an ART-initiated cycle, including all fresh and subsequent FET
cycles, until one live birth occurred or all embryos were used.
Other pregnancy outcomes assessed in the study included implantation
rate, CPR, ongoing pregnancy rate (OPR), LBR, ectopic pregnancy rate,
biochemical pregnancy rate, early spontaneous abortion rate (ESAR), late
spontaneous abortion rate (LSAR), singleton pregnancy rate, and
multiple pregnancy rate per fresh embryo transfer cycle. Implantation
rate was determined based on the number of gestational sacs detected by
ultrasound scan 5–7 weeks after embryo transfer divided by the number
of embryos transferred. Clinical pregnancy was defined as the presence
of a gestational sac with observed fetal heart by ultrasound 5 weeks
after embryo transfer, while ongoing pregnancy was defined as a
pregnancy with fetal heart activity detected by ultrasound after 12
weeks of gestation. Live birth was defined as at least one liveborn
baby at ≥ 20 weeks gestation with fresh embryo transfer. Early
spontaneous abortion was defined as miscarriage occurring during the
first trimester of pregnancy, while late spontaneous abortion was
defined as miscarriage occurring after the first trimester of pregnancy.
Multiple pregnancy was defined as more than one gestational sacs
detected by ultrasound scan 5–7 weeks after embryo transfer.
Perinatal outcomes, obstetric complications, andcongenital defects
Obstetric and perinatal complications, as well as congenital defects of
deliveries from an ART stimulation cycle, including all fresh and
subsequent FET cycles, were completely followed up. In this study, live
births after fresh embryo transfer were referred to as fresh live births
(FLBs); live births from all fresh and subsequent FET cycles were called
CLBs.
Obstetric complications included in this study were HDP, GDM,
pre-eclampsia, preterm premature rupture of
membranes, placenta previa,
polyhydramnios,
oligohydramnios,
postpartum hemorrhage, placental
abruption, and placenta accreta.
Perinatal outcomes included mode of delivery, gestational age, weight at
birth, neonatal asphyxia and infection, neonatal intensive care unit
(NICU) admission, and early neonatal death. Specifically, very preterm
birth and preterm birth were defined as a live birth or stillbirth
occurring before 32 and 37 gestation weeks, respectively. Very low birth
weight and low birth weight were respectively defined as birth weight
lower than 1,500 grams and 2,500 grams. Fetal macrosomia was defined as
birth weight > 4,000 grams.
Early neonatal death was defined as
the death of a liveborn baby within 7 days of birth.
Based on the International Statistical Classification of Diseases Q
codes (Q00-Q99)18, 10th Revision, congenital
malformations followed up in this study included cleft lip and cleft
palate and congenital malformations originating from the nervous,
circulatory, digestive, urogenital, and musculoskeletal systems.