A new study has found that even smoking just a few cigarettes a day can have detrimental effects on a baby's health.

"There is no 'safe' level of exposure from active smoking," said lead author Dr. Lucinda England of the National Institute of Child Health and Human Development in Bethesda, Maryland.

"We were able to detect detrimental effects on birth weight even among women smoking less than 5 cigarettes per day," she told Reuters Health. "Women likely need to quit entirely before their baby's birth weight approaches that of a woman who never smoked."

The study, which appears in the October 15th issue of the American Journal of Epidemiology, was conducted by the Centers for Disease Control and Prevention (news - web sites) in Atlanta, Georgia.

It has long been known that smoking during pregnancy is associated with decreased infant birth weight and other ill effects, including premature birth and sudden infant death syndrome (SIDS).

"Many pregnant women who are unable to quit smoking are able to cut down," said England. "We wanted to know if cutting down improves infant birth weight."

The team of researchers first compared the infant birth weights of women who cut down by 50% or more during pregnancy, but didn't quit, to those of women who didn't cut down. They adjusted for factors known to affect birth weight, such as the mother's age.

"We found no benefits to cutting back, except among women who smoked 5 cigarettes or less per day before they cut back," she said.

England and her team also took another approach in their investigation; they looked at the relationship between the number of cigarettes smoked per day in late pregnancy and birth weight, after adjusting for the number of cigarettes smoked per day in early pregnancy and other factors.

"We found that birth weight declined sharply from 1 to 8 cigarettes per day, but the effects of smoking on birth weight leveled off at more than 8 cigarettes per day," England told Reuters Health.

"This suggests that women smoking more than 8 cigarettes per day need to cut back to less than 8 cigarettes per day before infant birth weight improves," she said. "Women who already smoke less than 8 cigarettes per day should also benefit from cutting back."

Smoking is harmful to both pregnant women and their infants, but there are a number of resources now available to help women quit. Ideally, women should ask their health care providers about smoking cessation before becoming pregnant, explained England.

"A woman can still reduce the risks to her baby by quitting, even if she doesn't quit until after becoming pregnant," noted England.

"As far as reducing goes, we don't want to tell women who can't quit not to bother to cut back," she said. "However, we do want to stress that cessation is the best possible way to reduce risk to both mothers and their infants."

(China Daily October 22, 2001)