Three-quarters of female cigarette smokers and half of female marijuana smokers used these substances at least once during pregnancy, with 38 percent of cigarette smokers and 24 percent of marijuana smokers continuing to use throughout their pregnancy, Science Daily reported March 21.

University of Washington researchers Jennifer Bailey and Karl Hill also found that fathers rarely changed their alcohol, tobacco and other drug use at all during pregnancy, thus doing little to encourage behavioral changes among women.

The month-by-month study also found that even when women did quit using alcohol, tobacco or other drugs during pregnancy, use rates began rising again during the six months after pregnancy.

"The months after childbirth are critical for intervening with mothers," said Bailey. "For example, many already have done the hard work of quitting smoking and haven't smoked a cigarette in six months or more. We should support that effort so that they can continue as nonsmokers. However, we know if dad is smoking or drinking it is more likely that mom will resume smoking or drinking."

Researchers suggested that interventions be targeted to prospective fathers as well as pregnant women. "Pregnancy health-care providers need to talk to both fathers and mothers about their smoking, drinking and marijuana use," said Hill. "Pregnancy seems like such a great public-health opportunity to reach parents, but no one is talking to dads and this study shows that they are not changing their substance-use behavior. What dads do matters and we want them to reduce their substance use."

The research was published in the March 2008 issue of the journal Birth: Issues in Perinatal Care.