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Maternal use of pot and tobacco may boost birth defect risk



– New research suggests that pregnant users of both cannabis and tobacco may put their unborn children at higher risk of birth defects and small head circumference than if they used either alone.

Researchers also found that 13% of pregnant Medicaid recipients surveyed reported using both cannabis and tobacco within the past month.

The findings, presented at the annual meeting of the College on Problems of Drug Dependence, point to the importance of asking pregnant patients about cannabis use, especially if they smoke tobacco, said study lead author Victoria H. Coleman-Cowger, PhD, of the research organization Battelle, in an interview.

In some cases, in fact, pregnant women might think that marijuana is healthier than regular cigarettes, said Dr. Coleman-Cowger. She observed this phenomenon while conducting a smoking intervention study at a prenatal clinic that largely served poor, African American women.

“I learned that many participants were also smoking cannabis and felt that there was lower risk associated with cannabis use than with tobacco use,” she said. “Some women were decreasing their use of tobacco during pregnancy but increasing their use of cannabis.”

Dr. Coleman-Cowger’s observations at the clinic inspired the new study, which reports the findings of a convenience survey of 500 pregnant women.

The mean age in the group was 28, and 71% were black. Two-thirds were employed, and 29% were college graduates.

By comparison, the 45 women in the co-user group – who reported both cannabis and tobacco use in the past month – were 93% black, 42% employed, and 7% college graduates. (An additional 39 women reported tobacco use only, and 60 reported cannabis use only.)

Co-use also was correlated with “never married, being in the first trimester of pregnancy, not wanting to be pregnant when they were, past-month other substance use, and more frequent use of both cannabis and tobacco than either exclusive group,” Dr. Coleman-Cowger said.

In adjusted models, co-users were more likely (odds ratio, 5.7; P = .05) to give birth to babies with small head circumference than nonusers. The risks of giving birth to babies with small head circumference also were more likely among the tobacco-only users (OR, 4.8; P = .05) and cannabis-only users (OR, 2.0; P = .05), compared with nonusers. Birth defects also were more likely in the co-user group.

The study did not allow researchers to speculate on whether co-use may multiply risk vs. cannabis or tobacco use alone.

Dr. Coleman-Cowger said in light of the small sample size, the results should be interpreted with caution. One possible confounder is quantity of use, she said. “We did not assess quantity of use, but given our finding that frequency of use is higher among the co-use group, it could be that the co-use group is simply using more of each substance and thus impacting the health consequences.”

Current clinical practice guidelines do not suggest screening for cannabis use in pregnant women. But Dr. Coleman-Cowger said it’s “particularly important when tobacco use has been identified, though in states where substance use is considered child abuse, professional judgment should be utilized in terms of the legal implications of asking about use.”

More research is planned to better understand issues like quantity of use, and reasons why pregnant women co-use cannabis and tobacco, Dr. Coleman-Cowger said.

The National Institute on Drug Abuse funded the study, which Dr. Coleman-Cowger said is part of a larger project “to compare and validate screeners that assess prescription drug misuse and illicit drug use during pregnancy.” The study authors report no relevant disclosures.

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