MONDAY, Jan. 25, 2010 (HealthDay News) -- Babies of women who smoked during pregnancy have blood pressure problems at birth that persisted through the first year of life, a new study finds.
"What is of concern is that the problems are present at birth and get worse over time," said Gary Cohen, a senior research scientist in the department of women and child health at the Karolinska Institute in Stockholm, and lead author of a report in the Jan. 25 online edition of Hypertension. "They're not going away, they're getting worse."
The study led by Cohen compared 19 infants of nonsmoking couples with 17 infants born to women who smoked an average of 15 cigarettes a day during pregnancy. At one week of age, the infants of nonsmoking mothers experienced a 2 percent increase in blood pressure when tilted upright, with a 10 percent increase at one year. The pattern for the children of smoking mothers was reversed: a 10 percent blood pressure increase at one week, a 4 percent increase at one year.
And the heart rate response to tilting of the children of mothers who smoked was abnormal and exaggerated, the report said.
It's not possible to say whether the abnormalities seen in the babies will lead to trouble later in life, Cohen said. But, he noted, "the extent of the condition at one year suggests that it is not going to disappear quickly."
The reason why exposure to tobacco in the womb affects blood pressure is not clear, Cohen said. A leading possibility is that "smoking might damage the structure and function of blood vessels," he said, mainly by damaging the endothelium, the delicate layer of cells that line the interior of blood vessels.
Whether that damage will persist is not known. "We're only up to 12 months at the moment," he said. "We plan to follow them."
The damage seen in the Karolinska study is similar to that observed in babies born to mothers whose pregnancies were marked by such abuses as drug use, said Barry M. Lester, a professor of psychiatry and pediatrics at Brown Medical School, and director of the Brown Center for the Study of Children at Risk.
"Early kinds of natal insults can cause reprogramming of brain circuitry," Lester explained. He has led studies of the long-term effects of cocaine and amphetamine use during pregnancy. Many women who take such drugs also smoke, Lester added.
"When we isolated tobacco effects, we showed that there are inborn neural effects of tobacco exposure similar to what we see in cocaine and methamphetamine abuse," he said.
Some research has connected such problems to overproduction of cortisol, a "stress hormone" that plays an important role in regulation of blood pressure and the immune system, Lester said. "Cortisol overexposure is one hypothesis," he said. "There is a lot of evidence showing that too much cortisol is damaging."
It is a reasonable hypothesis, Cohen said. Babies born preterm have problems with blood pressure that have been linked to overproduction of cortisol by the adrenal glands, he noted, "and there are some parallels between tobacco smoke exposure and preterm babies of the same age."
Whatever the mechanism of damage, treatment to eliminate the problems after birth does not seem possible, Cohen added.
"What we know from studies in older kids is that even if you remove them from an environment of exposure to tobacco smoke, it is unlikely you will get full restoration of normal function," he said. "The best intervention to solve these problems is prevention. Women who are pregnant need to avoid exposure to tobacco smoke in the air. Passive smoke exposure can be as bad as being an active smoker."
Problems related to smoking during pregnancy are described by the U.S. Centers for Disease Control and Prevention.