American Journal of Epidemiology Advance Access originally published online on June 16, 2008
American Journal of Epidemiology 2008 168(4):427-433; doi:10.1093/aje/kwn140
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ORIGINAL CONTRIBUTIONS |
Interactions between Smoking and Weight in Pregnancies Complicated by Preeclampsia and Small-for-Gestational-Age Birth
1 Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA
2 Division of Epidemiology, Statistics and Prevention Research, National Institute of Child Health and Human Development, National Institutes of Health, Department of Health and Human Services, Bethesda, MD
Correspondence to Dr. Roberta B. Ness, University of Pittsburgh, Graduate School of Public Health, Room A527 Crabtree Hall, 130 DeSoto Street, Pittsburgh, PA 15261 (e-mail: repro{at}pitt.edu).
Received for publication February 20, 2008. Accepted for publication May 1, 2008.
Cigarette smoking protects against preeclampsia but increases the risk of small-for-gestational-age birth (SGA). Regarding body weight, the converse is true: obesity elevates rates of preeclampsia but reduces rates of SGA. The authors assessed the combined effects of smoking and weight among US women developing preeclampsia or SGA, studying 7,757 healthy, primigravid women with singleton pregnancies in 1959–1965. Smoking (never, light, heavy), stratified by prepregnancy body mass index (BMI (weight (kg)/height (m)2); underweight, overweight, obese), was examined in relation to preeclampsia and SGA. Among underweight (BMI <18.5) and normal-weight (BMI 18.5–24.9) women, smoking decreased the risk of preeclampsia (for heavy smoking, light smoking, nonsmoking, test for trend p = 0.002 for underweight and p = 0.009 for normal weight) after adjustment for age, race, and socioeconomic status. However, among overweight/obese women (BMI 
25), this trend was not apparent (p = 0.4). Among both underweight and overweight women, smoking significantly increased SGA risk (trend p < 0.001 for underweight and p = 0.02 for overweight/obese). Obesity eliminated the inverse association between smoking and preeclampsia but did not substantially alter the positive association between smoking and SGA. A possible unifying biologic explanation is discussed in this paper.
body weight; infant, small for gestational age; overweight; pre-eclampsia; pregnancy; smoking
Abbreviations: BMI, body mass index; OR, odds ratio; SGA, small-for-gestational-age birth