Can using marijuana affect fertility? Doctor weighs in

ATLANTA (FOX 5 Atlanta) - If you're pregnant or trying to conceive, you know smoking cigarettes is risky for you and your baby. But what about smoking marijuana?

Recreational marijuana use is now legal in 11 states. In Atlanta, Morehouse Healthcare reproductive endocrinologist Dr. Dorothy Mitchell-Leef says more young people are trying it, assuming it's harmless.

"People think, 'Oh, it's going to be fine for me because it's legal,'" Mitchell-Leef says.  "But, that has nothing to do with medicine, and nothing to do with the fact it can have an effect on people getting pregnant or when they get pregnant."

A study published in the Journal of the American Medical Association in June of 2019 found as many as 7% of pregnant women reported having used marijuana in the last month is 2017.

That is up from 3.4% of pregnant women self-reporting cannabis use back in 2002.

Another study published this year in the Journal of Addiction Medicine found 22.6% of urine drug screening samples collected from pregnant women at one major academic medical center tested positive for THC, the psychoactive ingredient in cannabis. 

Dr. Mitchell-Leef says there hasn't been a lot of research into how marijuana impacts fertility.  But, she warns, there is evidence it can cause hormonal changes that can make it harder for men to produce sperm and for women to ovulate.

Mitchell-Leef advises couples trying to conceive to avoid using marijuana, and emphasizes that includes men.

"If they already have a low (sperm) count or a low motility, that's going to compound the problem," Mitchell-Leef says. "So, we ask them to just back off and perhaps start again in about 2 to 3 months."

Much of the research centers around couples going through fertility treatment. 

One study found men who smoked marijuana had a 29% drop in their sperm count, while another, earlier this year, found men who had smoked pot at some point actually had a higher sperm count than men who had never smoked marijuana.

But, because smoking in general is tied to a higher risk of pregnancy loss, stillbirth and developmental problems in babies, Dr. Mitchell-Leef says she would stay away from marijuana.

"Definitely stop before you're trying to get pregnant, and definitely don't take it while you're pregnant or breastfeeding," Mitchell-Leef says.  "We want everybody to be as healthy as they can be.  We just healthy babies, and we want them to make it to term."

The Harvard T.H. Chan Public School of Health has taken a look a marijuana use and fertility treatment. Women who used cannabis while undergoing treatment with assisted-reproduction technology were more than twice as likely to have an unsuccessful pregnancy than women who didn't smoke marijuana or had used it before pregnancy treatment.