Using cannabis may put women at risk of losing their pregnancies, but may actually increase men's chances of fathering children, according to a new study published in the Human Reproduction journal.
The study enrolled 421 women who underwent assisted-reproduction technology (ART) at a Boston fertility center between 2004 and 2017, and 200 of their male partners. Out of all participants, 44 percent of women and 61 percent of men reported using cannabis at some point in their life. Three percent of women and 12 percent of men admitted to using cannabis while trying to conceive.
Over the course of the study, 317 women became pregnant, including nine women who were using cannabis regularly. Researchers found that 54 percent of cannabis-using women lost their pregnancies, compared to 26 percent of non-users.
Doctors were surprised to learn that cannabis actually had the opposite effect on male fertility. Of the 23 couples where the male partner actively used pot, 48 percent had a baby — that's compared to 29 percent of couples where the man did not smoke up.
The study highlights potential risks for cannabis users who wish to conceive, but the small data set makes it hard to conclude that these results hold true for everyone. The researchers only discovered three other clinical trials concerning the effects of cannabis on fertility. Two of these studies found that weed actually had no effect on couples trying to conceive naturally, but the third found that pot users using ART had lower egg yields and fertilization rates. But there was no negative impact on live births or pregnancies.
Recent studies report that the rate of weed use among pregnant women has doubled over the past 15 years, and many dispensaries recommend weed as a treatment for morning sickness. But there are very few studies that explore whether cannabis use actually poses risks to conception, pregnancies, or child development.
Some research has suggested that prenatal marijuana exposure can increase the risk of stillbirth, premature birth, or even potentially cause developmental problems or birth defects. But this data is far from conclusive. Other research has found that small amounts of THC can show up in a mother's breast milk, which might have negative effects on the child's neurological development, but again, the exact effects of a mother's weed use on her child are unclear.
“The bottom line remains that we know way too little about the reproductive health effects of marijuana,” said Dr. Jorge E. Chavarro of Harvard T.H. Chan School of Public Health in Boston, lead researcher of the fertility study, to Reuters. “The scarcity of information is particularly concerning given the concurrent trends of expanded legalization, increased perception that marijuana poses no health hazards and increased consumption among men and women of reproductive age, including among pregnant women.”