Prenatal exposure to secondhand tobacco smoke and impact on infant birth weight in two Chinese cities

Active cigarette smoking during pregnancy is a well-established risk for having a smaller baby. Whether secondhand smoke (SHS) has a similar effect is not as clear. This is a particularly important public health question in China, where approximately 65% of men and only 4% of women smoke. The primary goal of this study was to evaluate the association between prenatal secondhand smoke exposure and infant birth weight in China. The data collected for this cross-sectional study also afforded the opportunity to examine adverse birth outcomes in relationship to maternal weight factors, a secondary goal of this study since obesity is a pressing public health issue in China.;Four hospital obstetric wards took part in this cross-sectional study---two in Beijing and two in Changchun. Nearly 3,000 new mothers were interviewed post-partum about SHS exposure occurring in the prenatal period. Medical records were abstracted for data on infant weight, length, gestational age, maternal weight and height, and mother's reproductive history and pregnancy complications. Prenatal SHS exposure was analyzed as a risk factor for reduced birth weight among non-smoking women who gave birth to live-born singletons. Maternal weight status, as indicated by body mass index (BMI), and gestational weight gain were also analyzed in relationship to preterm birth, low birth weight, and fetal macrosomia.;Prenatal SHS exposure was not found to be associated with reduced mean birth weight in this population. The prevalence of self-reported SHS exposure was substantially lower than the prevalence of smoking among Chinese men, and self-reported levels of exposure were also lower than expected. Maternal prepregnancy obesity was significantly associated with preterm birth and macrosomia, but not low birth weight. Mothers who were underweight before pregnancy had a lower odds of macrosomia compared to normal weight mothers. Excess maternal weight gain during pregnancy was associated with lower odds ratios for preterm birth and low birth weight, and a higher odds ratio for macrosomia compared to moderate weight gain. Inadequate weight gain during pregnancy doubled the odds ratio for preterm birth.;Women in Beijing and Changchun may be more aware of environmental hazards to prenatal health than they are of the potential risks of excessive maternal weight and weight gain during pregnancy. The public health policies to reduce smoking and SHS exposure in China may have had an impact on smoking-related behaviors. Improved efforts are now needed to increase awareness about prenatal nutrition and health.