If a man habitually uses marijuana even as little as once a week, could that increase the risk of his partner experiencing a miscarriage in early pregnancy? A first-of-its-kind study suggests so.
By analyzing more than six years of lifestyle and behavioral data from 1,535 heterosexual couples actively trying to conceive, Boston University School of Public Health researcher Alyssa Harlow discovered that for men who use marijuana one or more times a week, their partner is twice as likely to miscarry than the partners of men who use marijuana less than once a week or not at all. The link persisted even after Harlow accounted for whether or not the men’s partners used marijuana themselves.
Most research on factors related to miscarriage has focused on women’s lifestyle or behavior, says Harlow, the study’s lead researcher. “But given that the human embryo is comprised 50 percent of the male’s genes, there’s been emerging interest in studying the role that men play,” she says.
Some studies have looked at caffeine and alcohol intake and found an association with increased rates of miscarriage, Harlow says. Until now, though, no one has looked at how male marijuana use affects miscarriage.
“There are [cannabinoid] receptors in human testicular tissue and sperm, and when a man uses marijuana, THC binds to these receptors,” Harlow says.
That knowledge, based on prior research examining the association between marijuana use and sperm quality, made Harlow and the other members of the research team curious about whether marijuana exposure could damage a man’s DNA or lower the quality of his sperm enough to result in a higher risk of his partner having a miscarriage.
“I’m really interested in the impact of substance use on pregnancy, and I’ve been watching the policy landscape change so rapidly around cannabis,” Harlow says. “I started reading more about marijuana and fertility, which helped us form the idea for this study.”
The analysis uses data from BU’s Pregnancy Study Online (PRESTO), a web-based study looking at lifestyle, dietary, and medical risk factors for pregnancy outcomes led by Lauren Wise, an SPH professor of epidemiology.
Harlow, who presented her findings this week at the annual meeting of the American Society for Reproductive Medicine, says that all forms of marijuana use—smoking, vaping, and ingesting—were part of the study, and that it’s not yet possible to parse those types of use apart to see if male use of one type has a higher miscarriage risk than the others.
For the women who miscarried, the median gestational time was six weeks of pregnancy. After eight weeks of pregnancy, the association between male marijuana use and miscarriage dropped off significantly. Harlow, an epidemiologist currently pursuing a PhD, says these findings support her hypothesis that male marijuana use compromises pregnancy at its early stages due to the changes it impacts on a man’s sperm. She says she’s looking forward to a peer review of the data and having the study’s results published in a scientific journal.
But she cautions that “one study does not a conclusion make. We need more studies before we can make any concrete recommendations. For couples trying to get pregnant, they should try to live as healthy a lifestyle as possible and talk to their doctor about marijuana use.”