Cohort composition
Of the 15,550,961 total live births in the US between 2015-2018, we
sequentially excluded pregnancies to primiparous women and women of
parity ≥3, multiple gestations, newborns with major malformations,
missing gestational age, 886 with gestational age <22 weeks,
and 120 with gestational age ≥45 weeks, as well as large for gestational
age births. We additionally excluded pregnancies with missing data for
TOL and previous caesarean delivery. After all exclusions, 3,755,798
non-anomalous, singleton live births delivered at 22-44 weeks remained
in the cohort (eFigure 1 ).