A re-examination of data from earlier studies suggests that exposure to second-hand smoke during pregnancy can be just as detrimental to a developing fetus as primary exposure through maternal smoking, according to a recent paper from Pitt’s Graduate School of Public Health.

In a study published in the online journal BMC Pediatrics, Stephen G. Grant, associate professor of environmental and occupational health, reports that both active maternal smoking and secondary maternal exposure result in similarly increased rates of genetic mutation that are basically indistinguishable.

“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,” said Grant, whose primary area of study is genotoxicity and the mechanisms of DNA repair. “These kinds of mutations are likely to have lifelong repercussions for the exposed fetus, affecting survival, birth weight, and susceptibility to disease, including cancer.”

This is a startlingly different conclusion from that reached by three previous studies looking at the potential effects of tobacco smoke exposure to babies in the womb, one of which Grant coauthored. Those papers largely discounted the effects of secondary—and sometimes even direct exposure through maternal smoking—or produced contradictory results.

The three previous studies looked at mutation rates at the HPRT gene located on the X chromosome in cord blood samples from newborns. Grant’s analysis pooled the studies’ data, looking for frequency of induced mutation as well as the resulting molecular spectrum of mutations. In particular, the new analysis redefines the “nonsmokers” used as controls to consider their second-hand exposure to tobacco smoke through other family members at home, at work, or in social situations at restaurants or even outdoors.

“Moreover, we found similarly increased induced mutation in women who had quit smoking during pregnancy, usually when they found out they were pregnant,” said Grant, who also is an assistant investigator at the Magee-Womens Research Institute. “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.”

Grant’s study was supported by funding from the National Institute of Child Health and Human Development and the University of Pittsburgh Competitive Medical Research Fund.