Data collection
The following information on each birth was extracted from the hospital
information system or birth record system: infant sex, date of birth,
delivery type (vaginal or cesarean), gestational weeks (GW) at birth,
maternal age, parity, pregnancy complications such as hypertensive
disorders of pregnancy (HDP) and gestational diabetes mellitus (GDM),
and major adverse pregnancy outcomes such as miscarriage and stillbirth.
We carefully checked the accuracy and quality of source data.
Implausible values and outliers were either corrected or recoded as
missing.