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. 2011 Jun;21(6):413-20.
doi: 10.1016/j.annepidem.2010.11.012. Epub 2011 Mar 21.

Prepregnancy body mass index, smoking during pregnancy, and infant birth weight

Michele La Merrill  1 , Cheryl R Stein, Philip Landrigan, Stephanie M Engel, David A Savitz
Affiliations

Prepregnancy body mass index, smoking during pregnancy, and infant birth weight

Michele La Merrill et al. Ann Epidemiol. 2011 Jun.

Abstract

Purpose: Smoking during pregnancy is strongly associated with increased risk of small for gestational age (SGA) and low birth weight, whereas elevated prepregnancy body mass index (BMI) is associated with a decreased risk of SGA and greater birth weight. We investigated the combined effect of prenatal smoking and prepregnancy BMI on risk of SGA and on birth weight.

Methods: A total of 34,928 singleton, term pregnancies in residents of New York City between 1995 and 2003 were evaluated in multivariable regression models of birth weight and risk of SGA.

Results: Increasing prepregnancy BMI reduced the risk of SGA and increased birth weight. The effect of prenatal smoking on birth weight and SGA diminished in women as their prepregnancy BMI increased, such that prenatal smoking did not significantly impact the risk of SGA among women who were overweight or obese before pregnancy. Prenatal smoking decreased mean birth weight by 187 g (95% confidence interval [CI] -337, -37) among underweight women, by 129 g(95% CI -170, -87) among normal weight women, by 46 g (95% CI -113, +20) among overweight women, and by 75 g (95% CI -162, +11) among obese women.

Conclusions: This study suggests that the effect of smoking during pregnancy on SGA and birth weight is present in underweight and normal weight women but markedly reduced among obese and overweight women.

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Figures

Figure 1
Figure 1
Interaction between prenatal smoking and prepregnancy BMI in relation to birth weight in 34,928 singleton term births, New York, 1995-2003. The multivariable model was adjusted for race/ethnicity, maternal age (≤ 20, 21-30, 31-40, >40 years), maternal education (< 12, 12 > 12 years), parity (0, 1, ≥ 2), and infant sex. Adjusted birth weights associated with women who did not smoke during pregnancy are depicted by squares/dashed line with 95% confidence intervals. Adjusted birth weights associated with women who smoked during pregnancy are depicted by circles/solid line with 95% confidence intervals.
See this image and copyright information in PMC

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