The Effects of Tobacco Use During and After Pregnancy on Exposed Children

Alcohol Research & Health, Winter, 2000 by Marie D. Cornelius

Long-Term Effects on Growth

The effects of prenatal tobacco exposure on older children's growth are not as clear as the effects on infants. Using data from the Collaborative Perinatal Project, Naeye (1981) detected a small difference in height and head circumference in exposed children at age 7. Rantakallio (1983) found that exposed children were shorter than nonexposed children at age 14, and Fogelman and Manor (1988) reported decreased height at ages 7, 11, and 23. In the latter study, the differences in height at age 23 were mediated by birth weight. These studies did not control for passive exposure to tobacco smoke or exposure to alcohol. A study of 714 three-year-old children found that the children of women who quit smoking during pregnancy were heavier and taller than those of women who did not quit (Fox et al. 1990). Adjustment for postpartum exposure to tobacco smoke reduced the difference in the children's weight, but had little effect on differences in height.

Other studies have not found growth retardation over the long-term (Fried and O'Connell 1987; Hardy and Mellitus 1972). In addition, one study that followed infants from birth through 6.5 months and 13 months found that prenatal alcohol exposure, rather than tobacco exposure, was associated with a slower growth rate when the exposed children were compared with unexposed children during the first 6.5 postpartum months. Although maternal smoking was correlated with shorter stature at 6.5 and 13 months, this effect was attributable to maternal

drinking during pregnancy (Jacobson et al. 1994), highlighting the importance of controlling for the effects of other drugs.

The MHPCD study of adult mothers and their children (Day et al. 1992), which controlled for prenatal alcohol and other drug exposures and current maternal tobacco use, found a significant inverse relationship between maternal tobacco use during pregnancy and the infant's weight, length, and head circumference at birth. At 8 months, only the infant's length continued to be associated with prenatal tobacco exposure. When the children were followed up at 18 months and 6 years, prenatal tobacco exposure was not related to any growth reductions after controlling for the appropriate covariates (Day et al. 1994). Similarly, Vik and colleagues (1996) found that the reductions in birth weight that were attributed to prenatal tobacco exposure were not evident when the children were 5 years old.

Prenatal tobacco exposure may not only be related to size deficits at birth, but may also be associated with disproportionate weight (for height) among both infants and young children. For example, a recent study of more than 200,000 births in Sweden found that prenatal tobacco exposure was significantly associated with reduced birth length and birth weight (Lindley et al. 2000). However, maternal smoking was also significantly associated with an increase in ponderal index, an indication of higher proportionate weight for height, when birth weight and gestational age were controlled for. Thus, the children of smokers tended to be shorter and have a higher ponderal index than children of nonsmokers. This finding is consistent with studies that have followed children after infancy. For example, Fried and colleagues (1999) found that prenatal tobacco exposure was related to an increased rate of obesity among 6-year-olds. The researchers proposed that this association was attributable to a preference for bottle -feeding among mothers who smoked during pregnancy. Vik and colleagues (1996) also reported a higher ponderal index and increased skinfold thickness (a measure of percentage body far) in children whose mothers smoked during pregnancy, compared with children whose mothers did not smoke. Researchers evaluating the MHPCD cohort of 6-year-old children of teenage mothers also found a positive association between prenatal tobacco exposure and increased skinfold thickness. Prenatally exposed children also had higher values on the body mass index and weight-for-height 7-scores, an indication that the children were overweight for their height (Cornelius et al. in press b). Bottle-feeding was not a significant factor. Thus, several recent studies indicate that prenatal tobacco exposure seems to alter the relationship between body length and weight. This finding is underscored by two studies that have found that prenatal tobacco exposure reduces the growth of the long bones in the fetus (Lindsay et al. 1997; Luciano et al. 1998).