The impact of prenatal care in the United States on preterm births in the presence and absence of antenatal high-risk conditions

OBJECTIVE: This study was undertaken to determine the association between prenatal care in the United States and preterm birth rate in the presence, as well as absence, of high-risk pregnancy conditions for African American and white women. STUDY DESIGN: Data were derived from the natality data set for the years 1995 to 1998 provided by the National Center for Health Statistics. Analyses were restricted to singleton live births that occurred at greater than or equal to 20 weeks' gestation. Multiple births, fetal deaths, congenital malformations, chromosomal abnormalities, missing data on gestational age, and birth weight less than 500 g were excluded. Multivariable logistic regression analyses were used to adjust for the presence or absence of various antenatal high-risk conditions, maternal age, gravidity, marital status, smoking, alcohol, and education. Prenatal care was considered present if there was one or more prenatal visits. Preterm delivery was defined as delivery at less than 37 completed weeks of gestation. RESULTS: For 14,071,757 births analyzed, 1,348,643 (9.6%) resulted in preterm birth. Preterm birth rates were higher for African American women than white women in the presence (15.1% vs 8.3%) and absence (34.9% vs 21.9%) of prenatal care. The absence of prenatal care increased the relative risk for preterm birth 2.8-fold in both African American and white women. There was an inverse dose-response relationship between the number of prenatal visits and the gestational age at delivery both among African American and white women. Lack of prenatal care was associated with increased preterm birth rates to a similar degree in the presence of pregnancy complications for both African American and white women, ranging from 1.6-fold to 5.5-fold for the various antenatal high-risk conditions. CONCLUSION: In the United States, prenatal care is associated with fewer preterm births in the presence, as well as absence of high-risk conditions for both African American and white women. Strategies to increase prenatal care participation may decrease preterm birth rates.