Exposure and other variables
Maternal demographics and lifestyle characteristics included maternal
age (≥35 years or no), parity (0 or no), education (university degree
and above or no), ART (intrauterine insemination (IUI); IUI with
ovulation induction but without in-vitro fertilization (IVF); IVF; IVF
with intracytoplasmic sperm injection (ICSI); ovulation induction
without IVF and vaginal insemination), pre-pregnancy body mass index
(BMI) categories (underweight, normal, overweight/obese).
Maternal pregnancy characteristics and complications included
gestational age at delivery, delivery mode (vaginal delivery, either
spontaneous or by vacuum extraction or forceps, and cesarean section,
either planned or by emergency), multiple pregnancy, gestational
diabetes mellitus (GDM), pregnancy induced hypertension (PIH),
hypothyroidism, preterm birth (<37 week), postpartum
hemorrhage (>500 mL after vaginal delivery, blood loss
>1000 mL after cesarean delivery), premature rupture of
membranes, ischemic placental diseases (composite of preeclampsia,
intrauterine growth retardation (IUGR), placental abruption and
stillbirth), placenta previa, abruptio placentae and postpartum
transfusion.
Newborn characteristics included fetal sex, birthweight, small for
gestational age (SGA) ≤10th, large for gestational age
(LGA) ≥90th according to Chinese sex- and gestational
age-specific birth weight standards[17],
macrosomia (>4000 g), low birthweight (<2500 g),
very low birthweight (<2500 g), sentinel congenital anomalies
(atrial septal defect, ventricular septal defect, esophageal fistula,
hypospadias), respiratory distress syndrome and hyperbilirubinemia
(>12 mg/dL).