FRIDAY, Oct. 12, 2001 (HealthDayNews) -- Women who smoke late in pregnancy can increase their unborn baby's birth weight if they cut down on their smoking, but not by a lot, says a new study.
Experts stress that pregnant women shouldn't consider the findings an excuse to continue smoking, which has been shown to significantly increase the odds of delivering a premature baby. Smoking also carries considerable health risks for the mother, including lung cancer and cardiovascular disease. A report on the study appears in the Oct. 15 issue of the American Journal of Epidemiology.
"There's not a safe amount that you can smoke. Even with a cigarette a day we can see an effect" on birth weight, says lead study author Dr. Lucinda England, a researcher at the National Institute of Child Health and Human Development in Bethesda, Md.
Smoking is a well-known cause of premature and thus underweight infants, who, in turn, are more likely to demand neonatal intensive care. While most survive the ordeal, many die and many more suffer later consequences of low birth weight, including physical and mental developmental problems.
Matthew Stefanak, health commissioner of Mahoning County in Youngstown, Pa., says "the frequency with which [maternal smoking] appears on birth certificates of low birth weight babies is pretty overwhelming."
Studies comparing smokers and nonsmokers "consistently report significant risks of [underweight] delivery for smokers and estimate the lower birth weights to be 200 grams (about 7 ounces), on average," Stefanak says.
Population studies, including one Stefanak and his colleagues conducted, "show a clear association between reported tobacco use of any amount" and roughly a doubled risk of delivering an underweight infant, he says.
In the new work, England and her colleagues looked at the effect on birth weight of reduced smoking in nearly 1,600 pregnant women in Colorado, Maryland and Missouri who ultimately delivered full-term babies. A full term is considered 40 weeks of gestation; infants are considered premature if born before 37 weeks.
Women who cut their smoking by half during pregnancy -- measured by how much they said they smoked and the amount of the nicotine byproduct cotinine was in their urine -- tended to have heavier babies, but the difference averaged an insignificant 32 grams, or a little over an ounce, the researchers say.
Women who smoked more during the last three months of pregnancy, when the baby grows the most, had progressively lighter infants, but the effect of additional cigarettes seemed to plateau after eight a day.
"Once women get to about a half a pack a day, if they smoke more than that there's no detrimental effects" on birth weight, says England. "But the flip side of that is that smoking that much has a detrimental effect. There's not a safe amount that you can smoke."
Dr. Orlando da Silva, a pediatrician at the University of Western Ontario in London, says he's not surprised that the effect of smoking on birth weight for full-term babies is small, since the biggest impact of tobacco use on fetal development is in triggering premature delivery.
Still, da Silva says, smoking during pregnancy can compound other problems, like infection and poor maternal diet.
What To Do
Pregnant women who smoke should talk with their doctors about quitting, England says. But since treatments such as patches or gum which also contain nictotine haven't been proven safe for unborn infants, women planning to become pregnant should consider stopping smoking before they conceive, she says.
For more on the harmful effects of smoking on pregnancy, check the New York State Smokers Quitsite or the American Lung Association.
