Ladies, listen up: Men who smoke weed may not make healthy babies.

Recreational marijuana is slowly but surely becoming legal across the United States. But just like the risks that come with drinking alcohol, risks also exist for smoking pot. For guys, one risk could be a big deal; it involves sperm. Which means if you want to have a baby, you need to know what it is.

A small study of just 24 participants recently published in the journal Epigenetics found, for the first time, that higher concentrations of tetrahydrocannabinol (THC) in urine corresponded to a lower sperm count. The study also concluded that pot smokers had changes in the genetic profile of their sperm, which earlier studies have linked to abnormal growth and even cancer.

Previous research has suggested that smoking marijuana can lower sperm count, or the number of sperm in semen when it’s ejaculated. This new study, however, is the first to link THC concentration in urine to sperm count.

The study also found that the sperm count of the men who didn't smoke weed was about twice as high as it was in the smokers. Yep, that’s a big difference.

Although this is super concerning, the researchers were even more worried about the changes in the genetic profile of the smokers’ sperm. These changes involved hundreds of genes that play a role in two very important outcomes: one that determines if the developing organs in an embryo reach full size, and one that regulates normal body growth during embryonic development. Previous studies have associated these types of alterations with cancer.

Just like with sperm count, the higher the THC level in a man’s urine, the more pronounced these genetic changes were.

"We don't yet know what that means, but the fact that more and more young males of child-bearing age have legal access to cannabis is something we should be thinking about," study author Scott Kollins, a professor in psychiatry and behavioral sciences at Duke University, said in a statement.

Because the study was so small, more research needs to be done to fully understand how marijuana use can affect sperm. Until then, heed the warnings of studies like this one and tell your guy to be mindful of how much he smokes. When it comes time to try for a bun in the oven, he’ll be glad you gave him a push to cut back.

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