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Amna R. Siddiqui,^1,2 Ellen B. Gold,¹ Xiaowei Yang,¹ Kiyoung Lee,³ Kenneth H. Brown,⁴ and Zulfiqar A. Bhutta⁵

¹Department of Public Health Sciences, University of California, Davis, California, USA; ²Department of Community Health Sciences, Aga Khan University, Karachi, Pakistan; ³College of Public Health, University of Kentucky, Lexington, Kentucky, USA; ⁴Department of Nutrition and Program in International and Community Nutrition, University of California, Davis, California, USA; ⁵Department of Pediatrics and Child Health, Aga Khan University, Karachi, Pakistan

Abstract
Background: Maternal exposure to wood fuel smoke may lead to impaired fetal growth due to hypoxia and or oxidative stress from smoke constituents such as carbon monoxide and particulate matter.

Objectives: We studied the risk of low birth weight (LBW) and reduced mean birth weight in relation to reported use of wood for cooking during the prenatal period, compared with natural gas (NG) .

Methods: We studied a historical cohort of women who had a singleton live birth in the years 2000–2002, from a semirural area of Pakistan. Infant's birth weight was obtained from records, and prenatal records had data for maternal body mass index and parity. Cooking habits, daytime sleep habits, and type of fuel used during the pregnancies in 2000–2002 were ascertained by a survey done in 2004–2005. We performed multiple linear and logistic regression modeling using propensity scores to adjust for confounding variables.

Results: Unadjusted mean (± SD) birth weight was 2.78 ± 0.45 kg in wood users, and 2.84 ± 0.43 kg (p < 0.06) in NG users. Infants born to wood users averaged 82 g lighter than infants born to NG users when weight was adjusted for confounders (p < 0.07) . The rate of LBW (< 2,500 g) was 22.7% among wood users compared with 15.0% in NG users (p < 0.01) , for an adjusted relative risk of 1.64 (95% confidence interval, 1.10–2.34) . The population attributable risk for LBW explained by wood use was estimated to be 24%.

Conclusion: Cooking with wood fuel during pregnancy, a potentially modifiable exposure, was associated with LBW and marginally lower mean birth weight compared with using NG.

Key words: birth weight, cooking habits, historical cohort, natural gas, pregnancy, propensity scores. Environ Health Perspect 116:543–549 (2008) . doi:10.1289/ehp.10782 available via http://dx.doi.org/ [Online 15 January 2008]

Address correspondence to A.R. Siddiqui, Department of Community Health Sciences, Aga Khan University, P.O. Box 3500 Stadium Rd., Karachi, Pakistan 74800. Telephone: 9221 486 4822, 9221 486 4811. Fax: 9221 4934294, 9221 4932095. E-mail: rehana.siddiqui@aku.edu

We are thankful to the U.S. National Institutes of Health for the financial support through grant 5R03 ES13159-2. We acknowledge support from the Fogarty International Center and the National Institute of Child Health and Human Development (research grant D43TW01267) .

The authors declare they have no competing financial interests.

Received 21 August 2007 ; accepted 14 January 2008.