Study design and data sources
We performed a cross-sectional analysis of non-anomalous, singleton live
births who were delivered in the US from 2015-2018 using natality data
assembled by the National Center for Health Statistics (NCHS). These
data are collected by delivery attendants and transferred to the NCHS
where they are cleaned, compiled, and de-identified. Demographic
characteristics, medical and health information, and newborn outcomes
were derived from the 2003 revision of the US standard certificate of
live birth. All data used in this study are publicly available in
de-identified form, and Institutional Review Board approval was
therefore not sought. The study followed the STROBE reporting guidelines
for cross-sectional studies.
The study population included women who delivered non-anomalous,
singleton live births between 22-44 weeks’ gestation. We restricted the
analysis to para 2 women to avoid confounding by number of prior
caesarean deliveries.