Maternal Substance Use and Developmental Impact: Tobacco

2015

Epidemiology of Tobacco Use in Pregnancy

According to the latest estimates, approximately 27 to 33 percent of women of childbearing age are smokers. Although increasing pressure is being placed on those who smoke to cease during pregnancy, the majority of expecting mothers fail to do so. The Centers for Disease Control (CDC) reports that 20 to 25 percent of expectant mothers continue their tobacco use during gestation. In the National Health Interview Survey, only 27 percent of women were able to immediately quit use when told that they were pregnant and an additional 12 percent were able to quit by the third trimester of pregnancy.

Growth Effects

Tobacco use by pregnant women raises concerns about potential teratogenic effects. Nicotine and its by-product, cotinine, are found in fetal serum and amniotic fluid at 15 percent higher concentrations than in maternal blood and last for 15 to 20 hours. Large amounts of nicotine and cotinine can be ingested by nursing infants of women who smoke. It has been well documented for many years that tobacco exposure affects fetal growth even after controlling for pertinent demographic and confounding variables. The earliest reported study on human infants who were prenatally exposed to tobacco smoke was done by Simpson (1957). She found that the incidence of low birth weight (<2,599 grams) among infants whose mothers smoked was twice as high as the incidence rate among mothers who did not smoke. The incidence of low birth weight in this study was dose related to the quantity of cigarettes smoked per day. Numerous studies have subsequently investigated the relationship between cigarette smoking and birth weight. In reviews of the effects of maternal smoking during pregnancy, the authors agree that there is overwhelming evidence to support the original finding that low birth weight is associated with maternal cigarette smoking. In addition, this dose-response relationship is found when controlling for such factors as age, parity, maternal weight gain, pre-pregnancy weight/height ratio, gestational age, socioeconomic status, and race. The risk of having a small-for-gestational-age (SGA) infant is two to four times higher for smokers, with smokers’ neonates weighing an average of 200 grams to 300 grams less than non-smokers’ infants. This effect was not found, however, among smokers who quit during their pregnancy. Hebel et al. () reported no effect on birth weight among women who quit before week 30 of gestation. Rantakallio () also reported no differences in birth weight between infants whose mothers quit smoking by the third trimester and infants whose mothers did not smoke during pregnancy.

Additional physiological variables that have been linked to tobacco smoke exposure after controlling for pertinent demographic and confounding variables include decreased gestational length, increased risk of spontaneous abortion, and sudden infant death syndrome. Among the long-term physiological effects of maternal smoking, increased incidence rates of bronchitis and pneumonia have been found (). Increased incidences of asthma and increased severity of asthmatic symptoms have also been associated with maternal smoking.

Cognitive Effects

Evidence for a general cognitive deficit during infancy and early childhood in children borne by mothers who smoked during pregnancy is mixed. General cognitive deficits have been found in some studies but not in others. Deficits in learning and achievement have also been posited as being associated with maternal smoking. Data from the National Collaborative Perinatal Project (NCPP) have shown that children of smokers have deficiencies in achievement, particularly in the areas of reading and spelling. No difference in achievement has been found in other studies comparing children of smokers and nonsmokers.

Language Effects

Investigations into verbal ability among children of smokers have yielded mixed results as well. Fried and Watkinson () found a difference between the receptive verbal abilities of children of smokers and nonsmokers, although not the expressive abilities of these two groups. This finding was later replicated, with a significant difference between the receptive language skills of children who were prenatally exposed to nicotine and children who were not. Although deficits in verbal processing have been found, these skills are known to be highly correlated with general cognitive ability. As such, it is difficult to determine the relative contribution of a general cognitive deficit from a specific deficit in verbal processing.

Auditory Processing Effects

Although there are few studies in this area, the evidence for a negative impact on the early auditory development of the children of women who smoked during pregnancy has been more consistent than that for most other outcomes. Poorer auditory habituation on standardized infant assessments has been found repeatedly. In polygraphic studies of sleep, Franco and colleagues () reported that infants of smokers, both newborns and 12-week-olds, showed decreased arousal to auditory stimuli compared to infants of nonsmokers. The evidence in older infants and children is more limited but consistent. These findings suggest that an underlying auditory processing deficit is associated with prenatal exposure to tobacco smoke that manifests in delays in early language development and later reading and academic skills.

Attention and/or Activity Level Effects

The role which early tobacco exposure plays in producing attentional deficiencies has been explored by a number of researchers. Results of these studies suggest that children who were exposed to tobacco during early development may have subtle deficits in their ability to control and regulate their behavior to meet environmental demands. Naeye and Peters () examined behavioral ratings of children whose mothers smoked during pregnancy and found that these children were rated as having lower attention spans and greater motor activity. Streissguth et al. () found that maternal cigarette use was significantly related to poorer attention and orientation to a vigilance task in children. Kristjansson et al. () also found deficits in auditory and visual vigilance and greater levels of motor activity among children of smokers.

More recently, a growing number of studies have reported associations between maternal smoking during pregnancy and externalizing behavioral problems during childhood and adolescence. It remains to be seen whether this possible causal relationship may be the result of uncontrolled confounding variables.

Social and Environmental Considerations

Some evidence suggests that the relationship between early tobacco smoke exposure and behavioral outcomes may be the consequence of a different psychosocial environment created by a parent who chooses to smoke. Differences have been found in the manner in which parents who smoke relate to their children when compared to parents who do not smoke. Fried and Watkinson () found that nicotine use was negatively related to maternal involvement with the child, opportunities for variety in daily routines, emotional/verbal responsivity to the mother, avoidance of restriction and punishment, organization of the physical and temporal environment, and provision of appropriate play materials. Furthermore, researchers have hypothesized that important personality characteristics, behaviors, and lifestyle variables differentiate smokers and nonsmokers. Smokers differ from nonsmokers on measures of anxiety, extroversion, nurturance, and deference. They report more symptoms of psychopathology, have more hospitalizations, lower status occupations, and more job changes than nonsmokers (). It remains to be seen whether any of these characteristics that exist between smokers and nonsmokers may be capable of mediating the relationship found between tobacco smoke exposure and teratogenic outcome variables.

Summary

No consistent evidence among available studies indicates that smoking during pregnancy is associated with major structural anomalies. Clear associations exist between prenatal cigarette smoking and low birth weight, perinatal death, alterations in fetal cardiorespiratory status, problems with long-term growth, and sudden infant death syndrome.

 

Selections from the book: “Handbook of the Medical Consequences of Alcohol and Drug Abuse” (2004)