Abstract
Purpose Maternal smoking during pregnancy is known to reduce infant birth weight. Epidemiologic evidence also supports a causal association between maternal second-hand smoke (SHS) exposure during pregnancy and reduction in infant birth weight, although the impact is less in magnitude. The primary purpose of this cross-sectional study is to examine the magnitude of this association in a population where both prevalence and dose of SHS exposure are thought to be higher than in U.S. populations. Methods Women who gave birth in four hospitals in two Chinese cities (Beijing and Changchun) between September 2000 and November 2001 were interviewed during their post-partum stay to quantify self-reported prenatal SHS exposure. Their medical records were reviewed for data on pregnancy complications and birth outcomes. Non-smoking women who delivered term babies (≥ 37 weeks gestation) were included in the study (N=2,770). Multiple linear regression was applied to determine the difference in mean birth weights between exposed and unexposed babies. Results Nearly a quarter of the women (24%) reported daily SHS exposure and 47% reported no exposure during the entire pregnancy, although 58% reported no exposure when asked about specific sources of SHS. Most of the women (75%) denied any SHS exposure from the husband smoking at home. The greatest deficit in infant birth weight associated with SHS exposure was -7 grams (95% CI -32, +19) for every hour/day exposed to husband smoking at home in Changchun. Interestingly, infants in Beijing had higher mean birth weights among the exposed than the unexposed for all measures of SHS exposure. Overall, no deficit in mean birth weight was observed between exposed and unexposed from all sources of SHS combined (+8 grams, 95% CI -1, +16). Conclusion No statistically significant reduction in birth weight was found with prenatal SHS exposure in this population. Future studies on SHS exposure and infant birth weight in China, where smoking is a critical public health issue, should emphasize more objective measures of exposure.
Highlights
The association between maternal active smoking during pregnancy and the risk of having a smaller baby has been well established since the 1960s based on epidemiologic studies [1,2,3]
The prevalence of smoking among men, and the prevalence of secondhand smoke (SHS) exposure among women, is significantly higher in China than in the U.S For this reason, and the fact that birth outcomes are of particular interest in a country where the one-child-per-couple family planning policy focuses attention on prenatal and newborn health, we examined the impact of prenatal SHS exposure on infant birth weight in northeast
Half of the mothers worked during their pregnancy, with slightly fewer working during the third trimester than the first trimester
Summary
The association between maternal active smoking during pregnancy and the risk of having a smaller baby has been well established since the 1960s based on epidemiologic studies [1,2,3]. The magnitude of this effect is, on average, a reduction of 250 grams in birth weight of babies born to smokers compared to babies born to non-smokers [4]. The relative risks of low birth weight with maternal prenatal smoking have ranged from 1.5 to 3.5, and an exposure-response relationship between increasing amount smoked and higher relative risk is seen in numerous studies [4]. Relative risks and odds ratios for delivering a smaller baby for those with prenatal SHS exposure compared to no or low exposure range from 0.5
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