t Most previous studies of preterm birth have
considered risk factors in isolation rather than examining
the collective impact of multiple candidate determinants.
In order to examine the combined impact of a set of
behavioral risk factors on the risk of preterm birth, we
analyzed data collected for the Pregnancy, Infection, and
Nutrition Study on a range of sociodemographic, behavioral,
and related factors. Women who received prenatal
care at selected clinics in central North Carolina and gave
birth in the period 1995–2005 were recruited into a prospective
cohort study, with 4,251 women providing the
required information on risk factors and pregnancy outcome.
A number of demographic and behavioral attributes
were modestly associated with preterm birth, with odds
ratios of 1.3–1.5, including age [35, African-American
ethnicity, height of 63 inches or less, parity 2?, and
delivery at the academic medical center. Despite weak
associations for individual risk factors, changes in a constellation
of behaviors during pregnancy predict substantial
shifts in the risk of preterm birth, suggesting a
reduction from 8 to 3% preterm among those with a lowrisk