There was a lower chance of conceiving “despite an increased frequency of intercourse,” the study abstract states.

If pregnancy was achieved, however, study authors found no differences in miscarriage rates between cannabis users and non-users.

Participants were part of a larger group of 1,228 women between the ages of 18 and 40 who had had one or two prior miscarriages. From 2006 to 2012, women participated for as many as six monthly cycles while trying to get pregnant and throughout pregnancy, if conception occurred, the NIH reports.

Women self-reported preconception cannabis use as many as four times over the course of the study: at baseline, after six months of follow-up or at the beginning of the conception cycle, and weeks four and eight of pregnancy.

If pregnancy was achieved, study authors found no differences in miscarriage rates between cannabis users and non-users. / PHOTO BY RAWPIXEL / ISTOCK / GETTY IMAGES PLUS

Researchers make clear that any conclusions about cannabis use and fertility should be tempered because the study included just a small number of cannabis users, amounting to five per cent. Only 1.3 per cent of participants used cannabis during the first eight weeks of gestation, the abstract notes.

Additionally, the NIH points out, researchers did not take into account cannabis use among the women’s partners, which could have influenced conception rates.

Researchers further point out that compared to non-users, cannabis users “had higher levels of luteinizing hormone and a higher proportion of luteinizing hormone to follicle stimulating hormone,” differences that “could potentially have influenced their likelihood of conception.”

All that said, “the authors say their results suggest that women trying to conceive should exercise caution with cannabis use until more definitive evidence is available,” according to the NIH. “Cannabis use continues to rise despite limited evidence of safety during critical windows of pregnancy establishment,” adds the study abstract.

The FDA advises against using cannabis “in any form during pregnancy or while breastfeeding.” / PHOTO BY ROSANOVA/GETTY IMAGES

Findings from research on cannabis use and pregnancy have been mixed. Some recent studies have linked marijuana use during pregnancy to conditions or behaviours in offspring, including psychotic-like behaviours and autism.

A study review published last year, however, concluded that “current evidence does not suggest that prenatal cannabis exposure alone is associated with clinically significant cognitive functioning impairments.”

Only a handful of studies have explored the impact of cannabis use on female fertility, notes a post from the Massachusetts General Hospital’s Center for Women’s Mental Health. “We will continue to recommend that women (and their male partners) who are pregnant or attempting to conceive should not use cannabis,” the post states.

The U.S. Food and Drug Administration, too, has remained steadfast in its advice to refrain from using CBD, THC and cannabis “in any form during pregnancy or while breastfeeding.”