Changes in Obstetric Interventions and Gestational Age Distributions in
the United States, 1990-2015: A Population Analysis of Official Natality
Records by State and Race/Ethnicity
Abstract
Objective To examine race/ethnic and state variation in changes in US
rates of labor inductions and rates of cesarean deliveries between 1990
and 2015, and to examine changes among a low-risk sample. Design
Population-based, retrospective. Setting 50 states and D.C. Population
All singleton first births in 1990 and 2015 from the National Vital
Statistics System Birth Data. Separate analytic samples are created for
births to Black (36 states, D.C.), Latina (42 states), and White women
(50 states, D.C.). Methods Calculate joint probabilities of birth by
weeks of gestation and by obstetric intervention status. Main Outcome
Gestational age at birth is measured in weeks and obstetric intervention
status was measured (1) vaginal delivery, no induction; (2) cesarean
delivery, no induction; and (3) labor induction. Results The probability
of birth between 37 and 39 weeks gestation increased substantially
between 1990 and 2015 among births to U.S. Black, Latina, and White
women. The increases were due to increases in labor induction at these
weeks gestation and due to downward shifts in the gestational age timing
of cesarean deliveries. Changes in the gestational age distribution did
not differ by race/ethnicity, and similar changes in both gestational
age and obstetric interventions were observed across U.S. states. The
changes were also observed among U.S. women at low-risk for obstetric
interventions. Conclusions Changes in gestational age distributions of
U.S. births and their underlying causes are likely national-level
phenomena and might not be responding to increases in maternal risk for
interventions.