Thinking about using cannabis during pregnancy? Think again.

Ottawa researchers warn about possible risks to babies

September 16, 2019

Cannabis and pregnancy infographic. 1.4% of Ontario women said they used cannabis during pregnancy between 2012 and 2017. 12% risk of preterm birth for cannabis users. 6% risk of preterm birth for non-users. Recreational cannabis is now legal in Canada, but that doesn't mean it’s safe for people who are pregnant or breastfeeding. Ottawa researchers found that self-reported cannabis use during pregnancy was linked to an increased risk of preterm birth. Their study was published in the prestigious medical journal JAMA, the Journal of the American Medical Association.

As cannabis becomes more socially acceptable, health-care researchers are mindful that some parents-to-be might think it can be used to treat morning sickness.

“It’s worth warning people of the risks of consuming cannabis during pregnancy,” said Dr. Mark Walker, Chief of the Department of Obstetrics, Gynecology and Newborn Care at The Ottawa Hospital, professor at the University of Ottawa and senior author on the study. “We hope our findings will help women and their health-care providers make informed decisions.”

Ottawa researchers reviewed data from every birth in Ontario between 2012 and 2017, before recreational cannabis was legalized.

The research team found that 1.4 percent, or 9,427 of the 661,617 women in the study, reported using cannabis during pregnancy. The researchers do not know how much cannabis the women were using, how often, at what time during their pregnancy, or how it was consumed.

Reported cannabis users had a 12 percent risk of preterm birth compared to 6 percent for non-users. Babies born preterm, before 37 weeks gestation, may have complications and need more care in the first few weeks of life.Researchers matched individuals who used cannabis to people with similar risk factors to tease out the health effects of cannabis. Risk of preterm birth was 7% for non-users and 10% for cannabis users. Risk of transfer to the NICU was 7% for non-users and 19% for cannabis users.

“In the past we haven’t had good data on the effect of cannabis on pregnancies,” said Dr. Daniel Corsi, Epidemiologist at The Ottawa Hospital and BORN Ontario. “This is one of the largest studies on this topic to date.”

Health Canada and the Society of Obstetricians and Gynaecologists of Canada recommend that it is safest to avoid using cannabis when pregnant and breastfeeding until more is known about the short and long-term effects.

Women who wish to stop using cannabis during their pregnancy should ask their health-care provider about services and support in their region.

Funders: This study was funded by the Canadian Institutes of Health Research. Research at The Ottawa Hospital is possible thanks to generous donations to The Ottawa Hospital Foundation. BORN Ontario is supported by the Ontario Ministry of Health and Long Term Care.

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