Higher levels of tetrahydrocannabinol, or THC — a chemical in marijuana that produces a euphoric feeling or “high” — was linked with changes in how eggs mature and a possible increase in chromosome malformations, according to the study published in the journal Nature Communications.

“The findings of this study are concerning and highlight the importance of a cautious approach in using cannabis when planning to conceive,” obstetrician Dr Jamie Lo, an associate professor of obstetrics, gynaecology and urology in the School of Medicine at Oregon Health & Science University in Portland, said in an email. She was not involved with the study.

“However, certain types of cannabis are typically more potent than others — cannabis extracts are typically more potent than cannabis flower,” Freeman, director of the Addiction and Mental Health Group at the university in the United Kingdom, said.

While people do try to adjust their consumption when the potency of their cannabis varies, “such as by adding less cannabis to their joint or inhaling less deeply,” these efforts fail to completely work, he added.

That means “higher potency products still deliver a larger dose of THC to consumers than lower potency products,” Freeman said.

Women may unknowingly harm the success of their future pregnancy by being exposed to higher THC levels than they intended, Lo said.

“Because it’s hard to know the specific level of THC in various cannabis products on the shelves, I advise my patients to consider safer alternatives to treat the symptoms they’re using cannabis for or at least try to reduce the frequency of their use.”