New research suggests that secondhand smoke exposure during pregnancy may be just as damaging to the unborn baby as the mother herself smoking during pregnancy.

Researchers pooled data from recent studies on genetic mutations in babies linked to tobacco- smoke exposure. They found the risk of genetic mutations associated with secondhand-smoke exposure was nearly identical to the risk tied to maternal smoking during pregnancy.

"This analysis shows not only that smoking during pregnancy causes genetic damage in the developing fetus that can be detected at birth, but also that passive -- or secondary -- exposure causes just as much damage as active smoking, and it is the same kind of damage," says researcher Stephen Grant, PhD, in a news release. Grant is associate professor of environmental and occupational health at the University of Pittsburg Graduate School of Public Health.

"These kinds of mutations are likely to have lifelong repercussions for the exposed fetus, affecting survival, birth weight and susceptibility to disease, including cancer," says Grant.

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New Warning for Secondhand Smoke

Researchers say the results of this study conflict with the three studies from which they gathered their data. Those studies largely discounted the effects of secondhand smoke on fetal development.

Each of the studies looked at the rates of mutation on the HPRT gene on the X chromosome in umbilical cord blood samples from newborns.

In the study, published in the current issue of BMC Pediatrics, researchers pooled data from all three studies and looked at the frequency of the tobacco-smoke-induced genetic mutation as well as other mutations triggered downstream by this mutation.

The reanalysis also included information on secondhand smoke exposure at home, work, or in social situations among the "nonsmokers" used as comparisons in the maternal smoking studies.

The study showed the increased rate of genetic mutations linked to secondhand smoke exposure was "virtually indistinguishable" from the rate linked to maternal smoking during pregnancy.

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Stop Before Getting Pregnant

"Moreover, we found similarly increased induced mutations in women who had quit smoking during pregnancy, usually when they found out they were pregnant," says Grant.

"Perhaps, like certain pharmaceutical warnings, it would be appropriate to caution women to quit smoking if they are pregnant or likely to become pregnant. It is equally imperative that workplace protection be offered to reduce passive exposure."

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By Jennifer Warner, reviewed by Michael W. Smith, MD

SOURCES: Grant, S. BMC Pediatrics, July 26, 2005 online edition. News release, University of Pittsburgh Medical Center.