Probability samples of area births versus clinic populations for reproductive epidemiology studies.
Studies of pregnancy outcome are generally based either on geographically defined populations, often from birth records, or on clinic or hospital populations. We compared women recruited into a clinic-based study, the Pregnancy, Infection, and Nutrition (PIN) Study, with women who resided in the geographical area of the study (Alamance, Orange, and Wake Counties in North Carolina) and gave birth over the corresponding time period (1996-2000). Clinic participants were more likely to be Black, younger, have lower education, be unmarried, have a more frequent history of adverse pregnancy outcome, obtain prenatal care later, and smoke more cigarettes. Despite that profile, the proportion of clinic participants delivering preterm was somewhat lower than among area women overall (10.8% vs. 11.3%). Black/White risk ratios for preterm birth were markedly different for area (1.6) vs. clinic women (1.1), whereas other predictors were similar. Patterns may differ across groups for many reasons, including self-selection of clinics and varying clinical practices.
Savitz
David A
DA
Carolina Population Center, University of North Carolina, Chapel Hill, NC, USA. david_savitz@unc.edu
Dole
Nancy
N
Kaczor
Diane
D
Herring
Amy H
AH
Siega-Riz
Anna Maria
AM
Kaufman
Jay
J
Thorp
John M
JM
D000328:Adult; D000367:Age Factors; D044383:Black People; D004522:Educational Status; D005260:Female; D006801:Humans; D009657:North Carolina / Q000453:epidemiology; D007752:Obstetric Labor, Premature / Q000453:epidemiology*; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D011295:Prenatal Care; D011336:Probability; D012307:Risk Factors; D012847:Single Person; D012907:Smoking / Q000009:adverse effects; D001741:Black or African American