Fetal Growth and Length of Gestation in Relation to Prenatal Exposure to Environmental Tobacco Smoke Assessed by Hair Nicotine Concentration
Jaakkola, Jouni J. K., Jaakkola, Niina, Zahlsen, Kolbjorn, Environmental Health Perspectives
We assessed the effects of prenatal exposure to environmental tobacco smoke on fetal growth and length of gestation. The study population consisted of 389 nonsmoking women who were selected from a population-based study in southeast Finland on the basis of questionnaire information after delivery (response rate 94%). The final exposure assessment was based on nicotine concentration of maternal hair sampled after the delivery, which measures exposure during the past 2 months (i.e., the third trimester). The exposure categories were defined a priori as high (nicotine concentration [is greater than or equal to] 4.00 [micro]g/g; n = 52), medium (0.75 to [is less than] 4.00 [micro]g/g; n = 186), and low as the reference category ([is less than] 0.75 [micro]g/g; n = 151). In logistic regression analysis, controlling for confounding, the risk of preterm delivery ([is less than] 37 weeks) was higher in the high [adjusted odds ratio (OR) = 6.12; 95% confidence interval (CI), 1.31-28.7] and medium exposure categories (adjusted OR = 1.30; 95% CI, 0.30-5.58) compared with the reference category, and there was a 1.22 (95% CI, 1.07-1.39) increase in adjusted OR with a 1 [micro]g/g increase in hair nicotine concentration. The corresponding adjusted OR was 1.06 (95% CI, 0.96-1.17) for low birth weight and 1.04 (95% CI, 0.92-1.19) for small-for-gestational-age. Key words: biomarkers, birth weight, hair nicotine, preterm delivery, small for gestational age, tobacco smoke pollution. Environ Health Perspect 109:557-561 (2001). [Online 21 May 2001]
The adverse effects of maternal smoking during pregnancy on fetal growth (1,2), as well as on the risk of preterm delivery (3) are well established. People exposed to environmental tobacco smoke (ETS) encounter mainly the same compounds as in the mainstream smoke inhaled directly by the smoker, although the concentrations and time patterns differ (2,4). Although individual studies have often been inconclusive (5-31), a recent meta-analysis by Windham and colleagues (32) suggests that exposure to ETS during pregnancy has a small effect on birth weight and the risk of term low birth weight. The effects on the length of gestation and risk of preterm delivery have been studied less (10,19,23,25), and the evidence of any effect is weak.
Assessment of exposure during a relevant time period and control of confounding are the most critical issues of validity in studies of the effects of ETS on pregnancy outcomes (32,33). In the first reports, exposure assessment was based only on information on the spouse's smoking (5-7,9,11-13,15-17,21, 22,24,26). Later studies collected information on multiple sources, such as other family members and work exposure or on quantity measured as daily duration of exposure or number of cigarettes smoked indoors (10,18-20,25,31). Questionnaire or interview information on sources of exposure is sensitive to information bias, especially if carried out after the delivery and if the accuracy of the smoking information is compromised due to inaccurate recall and variation of environmental conditions such as air change, area, and volume of the space. Few studies have used biomarkers of exposure such as serum cotinine (14,28,30) and saliva cotinine (29) measured during pregnancy or after delivery. Both of these biomarkers share a common feature of having a short half-life (4), and therefore they measure exposure only during a couple of days before sampling. Hair nicotine is a new promising biomarker; the method is noninvasive, and a sample of 0-2 cm from the proximal hair gives a good estimate of the exposure during the past 2 months (34,35). Taking into account the time frame, a hair sample at birth would describe exposure during the last trimester, which is considered the most important period for fetal growth. In a recent case--control study by Nafstad and colleagues (36), the risk of small-for-gestational-age births was related to the hair nicotine concentration of newborns and of their nonsmoking mothers after the delivery. …