Young women who smoke cigarettes, use marijuana or binge drink will often stop doing so while they are pregnant, but a partner’s pregnancy has no effect on young men’s pot use or binge drinking pattern, a new study shows.

The researchers also found that while many women reduced their substance use during pregnancy, it quickly returned to pre-pregnancy levels after the child was born.

The findings are “troubling, and highlight a need for preventive intervention,” Dr. Jennifer A. Bailey and colleagues from the University of Washington in Seattle write.

Efforts to reduce substance use during pregnancy focus almost exclusively on women, although research has shown that if a woman’s partner continues to drink or smoke during her pregnancy, she is more likely to do so as well, and will also be more likely to return to substance use after giving birth, the researchers point out.

Studies have also linked fathers’ cigarette and pot smoking to poor outcomes for children, including sudden infant death syndrome and childhood cancers, according to the report in the current issue of the journal Birth.

To better understand patterns of substance use during pregnancy for fathers as well as mothers, the researchers evaluated 412 men and 396 women who were 24 years old and were participating in a long-term study of behavior. Seventy-seven men and 131 women reported having a child during the previous three years.

About 35 percent of the men who became fathers reported binge drinking - consuming five or more drinks in two hours - which did not change during or after pregnancy. Similarly, the 20 to 30 percent of the men who smoked pot did not change their habits during or after the pregnancy.

However, men who smoked cigarettes were less likely to do so while their partner was pregnant, the researchers found, with rates dropping from 42 to 37 percent during a partner’s pregnancy. However it returned to pre-pregnancy levels within 10 months of the child’s birth.

Thirty percent of the women smoked before becoming pregnant, which decreased to 20 percent during their first trimester for 7 months after birth, but smoking rates rebounded within 1 year.

Six percent of the women reported binge drinking before pregnancy, which was reduced to 2 percent by the first trimester. However, rates of binge-drinking began rising again about three months after they gave birth, and were back to pre-pregnancy levels by the time their child was 20 months old.

One in 10 of the women who became mothers smoked pot before pregnancy, and 7 percent kept using marijuana while they were pregnant. The rates of marijuana use also returned to pre-pregnancy levels by the time their child was 2 years old.

Many women are able to abstain from substance use during pregnancy, Bailey and her team note, making the early postpartum month “a period of potentially stressful change in roles and responsibilities” a key opportunity for prevention. The findings also show that men need to get the message that continuing to use substances during a partner’s pregnancy can be harmful.

“Reductions in substance use among young fathers, both during their partner’s pregnancy and after the birth of their child, would likely increase the probability that mothers will relapse to use postpartum, and reduce children’s exposure to harmful substance use in the home environment,” the researchers conclude.

SOURCE: Birth, March 1, 2008.