People who use marijuana while trying to get pregnant may have more trouble conceiving

• People who used cannabis while trying to conceive were 41% less likely to get pregnant than non users, a study out of the National Institutes of Health found.
• The study only included 62 cannabis users and didn't account for male partners' substance use, which can influence fertility.
• Research on marijuana use before and during pregnancy is limited and mixed, but the FDA "strongly advises" pregnant and breastfeeding women to abstain.

Smoking pot or using other cannabis products while trying to get pregnant may lower your chances of conception, a small study out of the National Institutes of Health found.

The study, published Monday in the journal Human Reproduction, found that cannabis users were 41% less likely to conceive than non-users.

The study didn't look at women's partners' marijuana use, which could have also influenced fertility, and couldn't prove cause and effect.

Past research on the topic has been mixed. The researchers say that until more information is gleaned about how cannabis use in pregnancy, people trying to start a family should be aware that the drug may have an effect.

The study included 62 cannabis users and accounted for factors including age, BMI, and alcohol consumption

To conduct the study, researchers analyzed data from 1,228 women who'd had one or two miscarriages and were trying to conceive. They were followed for up to six monthly cycles while trying to get pregnant and, if they did conceive, during pregnancy.

READ MORE: Women are using marijuana to cope with pregnancy symptoms like nausea even though the FDA warns against it

The study participants reported whether they used marijuana, pot, or hashish in the past year, and also provided urine samples when the study began and six months later if they still weren't pregnant. Those who did get pregnant provided urine samples at the time of a positive pregnancy test.

Only 62 women, or 5% of the participants, were cannabis users based on self-report or urine sample.

In addition to finding that they were 41% less likely to conceive than non-users, the researchers found that, over the course of the study, 42% of those who used cannabis got pregnant while 66% of non-users did. Using cannabis didn't seem to affect chances of pregnancy loss, however.

The researchers accounted for other factors that could have affected the results, like age, race, BMI, education, alcohol use, and antidepressant use. When they also looked at how factors including income, employment status, and stress may have played a role, their findings were similar.

READ MORE: Women who used marijuana during pregnancy were 1.5 times as likely to have a child with autism, the largest study of its kind has found

However, other factors could be at play, like their partners' substance use, as research suggests male cannabis use can negatively impact fertility.

The study authors say differences in reproductive hormones between cannabis users and non-users could help explain their findings. They also pointed to animal studies showing that cannabis use may affect the lining of the uterus, making pregnancy more difficult.

"These results highlight potentially harmful associations between cannabis use and reproductive health outcomes, and the need for expanded evidence regarding the effects of cannabis use on reproductive health in the current climate of increasing legalization," the write.

Cannabis may also have negative effects during pregnancy, but use among pregnant people is on the rise

The current study adds to a mixed body of research on cannabis use and fertility, though it's stronger than some in the sense that it collected urine samples rather than only relying on women to report their substance use.

But it's difficult to study marijuana's effect on fertility in women since there's not a clear measure to evaluate, like semen in men.

Research on cannabis use during pregnancy is limited and mixed, too. Some have linked marijuana use in pregnancy to consequences in their children including lower birth weights and cognitive issues like lower IQs, attention problems, and more impulsiveness.

However, a 2020 review of three decades of research on the topic called that conclusion into question, showing that cannabis use in pregnancy had little effect one way or the other on kids' cognitive outcomes. Even in cases where children of cannabis users perform more poorly than non-users, they are still in the normal range of cognition, the study authors point out.

Still, the US Food and Drug Administration has "strongly advised" women to abstain from CBD and THC, two of the main compounds found in cannabis, while pregnant or breastfeeding."

At the same time, marijuana use during pregnancy in the U.S. has been on the rise, growing from 2.9% in 2002 to 5% in 2016, according to a January 2019 letter in JAMA Pediatrics.