Smoking's Effects On Pregnancy Not Mitigated By Prenatal Vitamins

BUFFALO, N.Y. -- Pregnant women who continue to smoke, thinking their prenatal vitamins will offset the known adverse effects of smoking on the developing fetus, are deluding themselves, a new study by University at Buffalo researchers shows.

Live-birth data and personal information from more than 9,000 smoking and non-smoking women who took part in the 1988 National Maternal and Infant Health Survey showed that the risk of adverse outcomes were higher among smokers than non-smokers, as expected, and that the risks for smokers were similar whether or not they took vitamins.

The study appears in the current issue of Annals of Epidemiology.

"This paper is very important for the public health, because it shows that women who smoke and take vitamins do not really minimize the risk of pre-term birth, low-birth weight babies and babies who were smaller than average for their gestational age, all conditions that are associated with smoking," said Germaine M. Buck. Ph.D., associate professor of social and preventive medicine and co-author of the study with doctoral student Tiejian Wu, M.D.

"As far as we can tell, this is the first paper to show this. The message is, 'Do not smoke during pregnancy, because vitamins won't help to negate smoking's effects.'"

Multivitamins are a common part of prenatal care in the U.S. The 1980 National Natality Survey found that 95 percent of married mothers in the survey used supplements during pregnancy. Studies also have shown that women who smoke during pregnancy are more likely to take vitamins -- and to take more vitamins -- than women who don't, possibly in an effort to offset the reported adverse effects of smoking.

To determine if multivitamins are effective in reducing the risk of these adverse effects, Buck and Wu analyzed data from 9,402 women regarding pre-term births, 9,395 women for risk of very-low or moderately-low weight babies, and 9,363 women for the risk of small-for-gestational-age infants, plus self-reported information on smoking and prenatal vitamin intake.

Results showed no significant decrease in risk of pre-term births, lowered birth weights or children who were small for their gestational age among women who smoked during pregnancy and also took vitamins.

"These findings show that taking vitamins doesn't substitute for giving up smoking during pregnancy," Buck stated.

• Among 9,402 women, nearly one-quarter said they continued to smoke after learning they were pregnant.

• 75 percent reported taking vitamins regularly during their pregnancies.

• Women who used vitamins regularly during pregnancy tended to be older, married, better educated, and have larger family incomes than women who did not.

• Women who smoked 1-9 cigarettes a day had a 70 percent increase in risk of bearing very-low birth weight babies than women who did not smoke.

• The risk of small-for-gestational-age babies in smokers was more than twice that of non-smokers.

Pauline Mendola, Ph.D., formerly with the UB Department of Social and Preventive Medicine and now with the U.S. Environmental Protection Agency, also contributed to the study.