NIDA-funded researchers have added to the accumulating scientific evidence that women's smoking during pregnancy adversely affects their children's health and development. Two new studies have linked prenatal tobacco exposure to negative behavior in toddlers and smoking experimentation by pre-adolescents.
In a study conducted by Dr. Judith Brook, Dr. David Brook, and Dr. Martin Whiteman of the Mount Sinai School of Medicine in New York City, mothers who smoked during pregnancy indicated that their toddlers exhibited more negative behaviors - impulsiveness, risk-taking, and rebelliousness - than mothers who did not smoke during pregnancy reported among their children.
A study conducted by NIDA-funded researchers Dr. Marie Cornelius and Dr. Nancy Day demonstrates that, even more than growing up in a home where the mother smokes, prenatal exposure to smoke may predispose children to early smoking experimentation. Dr. Cornelius, Dr. Day, and their colleagues at the University of Pittsburgh School of Medicine found that not only does such exposure to maternal smoking predict early experimentation, it also appears linked to child anxiety, depression, and behaviors such as hitting and biting others.
Previous studies have supported a link between prenatal smoking exposure and behavioral problems in later childhood and adolescence (see "Drug Abuse and Conduct Disorder Linked to Maternal Smoking During Pregnancy,"). Combined with earlier results, the new studies suggest that prenatal smoking contributes to a train of developmental difficulties and health risks that begin at an early age.
The Mount Sinai study included 99 mothers who smoked and their 2-year-old children. The mothers are participants in a large community study that Dr. Judith Brook has been conducting with Dr. Patricia Cohen of Columbia University in New York City for the past 25 years. In the new study, the mothers answered a questionnaire that elicited information about their children's behaviors and their own smoking histories, alcohol and drug use, personalities and attitudes, styles of child-rearing, and socioeconomic characteristics.
Fifty-two of the women reported that they had smoked while pregnant, and 47 said they either stopped smoking during pregnancy or did not begin to smoke until after they had given birth. The mothers who smoked during pregnancy scored their children higher on the questions that measured toddler negativity.
The mother's disciplinary style also was strongly linked to a toddler's negative behavior. However, when the researchers adjusted for this factor in the analysis, they determined that a mother's smoking during pregnancy independently increased the estimated risk of negativity at age 2 by fourfold.
"We found three major maternal risk factors related to toddler negativity," says Dr. Brook. "They are maternal smoking during pregnancy, conflicts between the mother and child, and the mother's use of power-assertive discipline, such as hitting the child. We can speculate that maternal smoking during pregnancy causes disturbances in the neurophysiological functioning of the fetus," says Dr. Brook. "This, in turn, could precipitate the toddler's negative behavior."
The potential implications of these findings reach beyond early childhood. Previous studies have demonstrated that toddlers who display negative behaviors are more likely to use drugs, exhibit delinquent behaviors, and achieve less as adolescents and to develop severe mental health problems later in life.
Early Experimentation With Tobacco
Although the effects of maternal smoking on childhood behaviors have been studied, few studies have investigated the connection between maternal smoking and childhood experimentation with tobacco. The connection is important because the earlier a person starts smoking, the more likely he or she is to become a regular smoker, become addicted, and suffer the long-term adverse health effects of smoking.
Dr. Cornelius and her colleagues interviewed 589 10-year-olds. Six percent of the children said they had tried cigarettes, smokeless tobacco, or both. Most of the reported tobacco use was experimental; only a few children had used tobacco more than a few times.
In this prospective study, begun by Dr. Day in 1982, the children's mothers have been providing researchers with information about themselves, and they reported on their smoking at the time they were pregnant with the children who are now 10. Putting data from the children together with those reports, the researchers estimated that maternal smoking of at least a half-pack of cigarettes per day during pregnancy increased by fivefold the likelihood that a child would have tried tobacco by age 10. The only factor that produced a greater risk of early experimentation was exposure to smoking within the child's peer group.
It is not yet clear exactly why these factors are related to early experimentation. "Perhaps the nervous system damage caused by maternal smoking may later be expressed as impulsivity, inattention, aggression, depression, and/or anxiety and may create a vulnerability in the child that could contribute to poorer adjustment and an increased likelihood of early initiation of tobacco use," Dr. Cornelius says.
Dr. Cornelius notes that in her study, the 10-year-olds who were exposed prenatally to tobacco were more likely to have experimented than those whose mothers were current smokers. This finding reinforces the hypothesis that a physiological effect of prenatal exposure to smoking, rather than a genetic vulnerability affecting both mother and child, may be an important link between mothers' smoking during pregnancy and early childhood experimentation.
Brook, J.S.; Brook, D.W.; and Whiteman, M. The influence of maternal smoking during pregnancy on the toddler's negativity. Archives of Pediatric and Adolescent Medicine 154(4):381-385, 2000.
Cornelius, M.D.; Leech, S.L.; Goldschmidt, L.; and Day, N.L. Prenatal tobacco exposure: Is it a risk factor for early tobacco experimentation? Nicotine & Tobacco Research 2:45-52, 2000.