Marijuana’s active ingredient was linked to higher rates of chromosomal abnormality in early embryos, according to new research, potentially providing new insight into the link between cannabis use and female fertility.
The new paperpublished Tuesday in Nature Communications, showed that the presence of THC, or tetrahydrocannabinol, was associated with lower rates of embryos that contain the correct number of chromosomes. Separately, exposing immature egg cells to THC disrupted their ability to sort chromosomes.
The paper was based on two studies, both conducted by the same research team in Toronto. The first, a lab study, exposed oocytes, or immature human egg cells, to THC and measured their chromosomal development. The second, a retrospective study that used real-world data from patients undergoing IVF treatment, compared outcomes between those whose follicular fluid tested positive or negative for THC.
Both studies’ results “pointed in the same direction,” said the paper’s lead author, Cyntia Duval, a researcher affiliated with the University of Toronto and the CReATe Research Program, the scientific arm of a Toronto fertility clinic.
“I think that’s the biggest strength of this paper — that we used two studies to answer the same question,” Duval said. “The main conclusion would be that THC induced chromosomal segregation errors in both oocytes and embryos.”
With marijuana now legal in Canada and much of the U.S., and overall use rates climbing steadily, some public health experts have warned that rising cannabis use could yield unintended consequences. Many previous studies have found that marijuana use can negatively affect male fertility. Little is known, however, about the impact of cannabis use on female fertility.
The findings align with the broad understanding about links between substance use and reproductive health, said Jamie Lo, an associate professor of obstetrics and gynecology at Oregon Health & Science University, who was not involved in conducting the research.
“This is consistent with what we know about other substances, including cannabis, and what we know about cannabis in pregnancy, as well as cannabis in male fertility and male reproductive health,” she said. “That exposure, especially to higher levels of cannabis or specifically THC, can be associated with worsening fertility, increased reproductive complications, and potentially increased adverse outcomes for pregnancy.”
In the lab study, THC exposure led to a 9% increase in rates of aneuploidy, or an embryo containing an improper number of chromosomes, and more than doubled the rate of spindle abnormalities, which are crucial to segregating chromosomes during cell division. In the retrospective analysis, just 60% of embryos in the THC-positive group had the proper number of chromosomes, compared to 67% in the THC-negative group.
Duval cautioned, however, that the study was specific to patients undergoing IVF treatment who have been exposed to high levels of hormonal stimulation, meaning that the study’s results may not be generalizable to the broader population. Moreover, she said, countless people who consume marijuana have successfully conceived, meaning the public should treat her study’s results as a data point, not a red flag.
“It’s not that cannabis will make you infertile,” Duval said. “It’s just to bring a little bit more caution around that — but I don’t want any type of fear-mongering.”
While Lo, a physician-researcher, was also nuanced in her interpretation of Duval’s findings, she said she already counsels patients trying to conceive to avoid cannabis.
“It’s important that patients try to abstain from cannabis use when trying to conceive, but for those that cannot, this still offers an opportunity for harm reduction by reducing the amount they’re using to mitigate adverse outcomes to themselves and their fertility, their reproductive health, and their babies,” Lo said.
Limitations of the in vitro study include an inability to stratify the oocytes by patient age, even though age is an importation factor in the cells’ ability to mature in a lab setting. The retrospective study was also limited by a lack of data about specific substance use behavior, including the presence of other substances and the frequency or dosing of cannabis use among those whose follicular fluid contained THC.
Still, the two studies break new ground in measuring the impact of cannabis on reproductive health. Numerous previous studies had shown marijuana use — generally, heavy use — and the presence of THC had a negative effect on male reproductive endpoints, like sperm count and concentration, and on outcomes for women who used cannabis while pregnant.
“I remember this project started in my head in 2018, when the Canadian government legalized the use of recreational cannabis in Canada,” Duval said. “I was surprised to see the amount of data on male fertility, on pregnancy, but this big gap of knowledge in female fertility, and that’s what this study aimed to answer.”
STAT’s coverage of chronic health issues is supported by a grant from Bloomberg Philanthropies. Our financial supporters are not involved in any decisions about our journalism.
