Babies exposed to tobacco in utero more irritable, difficult to soothe

Dec 1 2008

Previous studies have shown that babies exposed to tobacco in utero are more likely to have a low birth weight and are at increased risk for sudden infant death syndrome.

Now new research by The Miriam Hospital reveals that these babies are also less likely to self-soothe and are more aroused and excitable than newborns whose mothers did not smoke during pregnancy.

Researchers from The Miriam Hospital's Centers for Behavioral and Preventive Medicine say early identification and targeted intervention efforts aimed at both infants and parents may help prevent possible disruption in early maternal-infant bonding and, ultimately, long-term adverse outcomes. The study is published online by the Journal of Pediatrics .

"A baby who is harder to soothe and more irritable could be more difficult to take care of and could potentially affect the developing mother-child relationship, especially for mothers who are already stressed and have fewer resources," says lead author Laura Stroud, PhD, a psychologist with The Miriam Hospital's Centers for Behavioral and Preventive Medicine. "We need better treatment programs to help women not smoke during pregnancy, to keep them from starting smoking after the baby is born, and to help them take care of an excitable or colicky baby."

Between 11 and 30 percent of women continue to smoke during pregnancy, according to the Centers for Disease Control and Prevention. In addition to the physical side effects, tobacco exposure in utero has also been linked to long-term adverse neurobehavioral outcomes in children, including conduct disorder and hyperactivity. However, researchers say relatively less attention has focused on the effects of maternal smoking on newborn neurobehavior.

In the study, Stroud and colleagues from Women & Infants Hospital in Providence, RI, and the Warren Alpert Medical School of Brown University focused on newborns between 10 and 27 days old. The researchers decided on this infant age range because it is well past the half-life of nicotine, meaning the acute effects of nicotine withdrawal were unlikely to be a factor in the study. All 56 babies – 28 smoking-exposed and 28 unexposed – were healthy and full-term. Maternal social class, age and alcohol use were similar in each group.

Mothers in the study were assigned to the smoking or non-smoking group based on self-reports of cigarette use during pregnancy assessed shortly after babies were born. This was verified biochemically by measuring cotinine, the primary metabolite of nicotine, in the mother's saliva. Cotinine is readily passed from mother to infant, with the baby absorbing nearly as much as the mother does.

On average, the number of cigarettes mothers smoked each day decreased over the course of the pregnancy, from about 15 cigarettes per day in the first trimester to approximately five cigarettes in the third trimester.

Postnatal smoke exposure was quantified by infant saliva cotinine levels. All infants were then assessed using the Neonatal Intensive Care Unit (NICU) Network Neurobehavioral Scale, a tool developed for the National Institutes of Health to measure the effects of prenatal drug exposure in infants, including withdrawal and general signs of stress.

According to the study's findings, smoking-exposed infants showed a greater need for handling, or external intervention, in order to be soothed and calmed down. These babies also tended to be more easily aroused and excitable.

"Although the effects of maternal smoking at 10 to 27 days were subtle, in combination with a high-stress postnatal environment and deficits in parenting, they could represent early precursors for long-term, negative behavioral outcomes," says Stroud, who is also an assistant professor of psychiatry (research) at Alpert Medical School.