More Smoke Less Baby Maternal ETS Exposure Means Low Birth Weight Preterm Delivery

These days it’s impossible to argue that smoking during pregnancy is good for the baby, but research is beginning to show that environmental tobacco smoke (ETS), too, may cause adverse effects in the unborn child. Jouni J. K. Jaakkola of the Nordic School of Public Health in Göteborg, Sweden, and colleagues used hair samples to gauge ETS exposure among new mothers during the last trimester, the period of greatest fetal growth [EHP 109:557–561]. They found evidence that maternal ETS exposure increases the risk of preterm delivery and affects fetal growth. This study is the first to support an increased risk in preterm delivery linked to ETS exposure. Nicotine in hair, which accumulates through both internal and external routes, is considered a promising new biomarker for ETS exposure. Hair nicotine reflects exposure over the previous 2 months, whereas serum and saliva concentrations of cotinine (a metabolite of nicotine) have a half-life of only 2–3 days. This means that hair samples taken from mothers at delivery can tell how much ETS exposure the fetus received during the third trimester, the period when the fetus does the most growing in the least time, doubling in size. Hair nicotine may therefore provide an antidote to the problems (such as inaccurate subject recall) associated with the questionnaires and interviews often used in exposure assessments. Hair sampling also has the benefit of being noninvasive. The scientists recruited 389 nonsmoking Finnish women from among all mothers who had given birth in two hospital districts between May 1996 and April 1997. The day after delivery, the women completed a questionnaire on maternal health, smoking and exercise habits, and details of their home and work environments. They also provided hair samples. A little over one-third of the women reported exposure to ETS in the home and/or at work. Another third of the women were married to smokers but reported no exposure to ETS. The rest were married to nonsmokers and reported no exposure to ETS. For purposes of the study, the scientists defined low birth weight as less than 3,000 grams, which is higher than the traditional cutoff of 2,500 grams. The 2,500 gram cut point has been used since the early 1900s, although babies born today are heavier on average. Thus, says Jaakkola, including a larger proportion of newborns from the lower birth weight end conveyed the idea of studying the smallest babies but increased the number of outcomes and the power of the study. The team also considered whether children were small for gestational age and whether they were delivered preterm. Jaakkola and colleagues found that mean birth weight among the women was consistent with the Finnish average; only 7 of the children were what is traditionally considered low birth weight (less than 2,500 grams). But they also found that the greater the mother’s hair nicotine measurement, the lower the child’s mean birth weight and the higher the prevalence of adverse pregnancy outcomes. Of children of mothers in the highest exposure group, 15.4% had low birth weight, 9.8% were small for gestational age, and 9.6% were preterm, compared to 9.9%, 8.0%, and 2.7%, respectively, for children of mothers in the lowest exposure group. The researchers found that ETS exposure at work correlated with preterm delivery more than home exposure did, although hair nicotine due to reported exposures at both locations was similar, an irregularity that the team theorizes may be due to unknown confounding factors in the workplace. –Susan M. Booker