Cannabis use among women who were about to conceive children nearly doubled following B.C.’s legalization of cannabis in 2018, a new study from UBC finds.

The findings show a 71 per cent increase in self-reported cannabis use by those in the preconception period (the three months before becoming pregnant) after adjusting for factors like age, education, relationship status, income and history of mental health disorders between two sample groups.

Cannabis use during pregnancy remained statistically unchanged.

“I was very surprised when I saw the huge increase in preconception use,” said Dr. Hamideh Bayrampour, the study’s lead author. “It’s a very dramatic change over a period of less than two years.”

It’s not recommended for people during preconception to use cannabis, to avoid any potential early exposure to the baby.

Researchers believe the rise in the rate of cannabis use after legalization could reflect a broader society-wide increase in the use of cannabis or an increased general perception that it’s safer to use cannabis while considering a pregnancy. It could also show that people feel more comfortable reporting that they use cannabis.

The multi-phase study led by Dr. Bayrampour, an assistant professor in UBC’s department of family practice, sampled 819 participants in two groups: one pre-legalization group of 494 pregnant women surveyed between May and October 2018, and one post-legalization group of 325 pregnant women surveyed between July 2019 and May 2020.

Any pregnant person above the age of 19 residing in B.C. was eligible to participate.

From pre- to post-legalization, the prevalence of self-reported use of cannabis during the preconception period increased significantly from 11.74 per cent to 19.38 per cent. Cannabis use during pregnancy increased from 3.64 per cent to 4.62 per cent, which the researchers did not consider statistically significant.

Although the effects of preconception cannabis use are not yet well known, the study highlights that according to the current evidence, prenatal cannabis use is linked to a 50 per cent increased risk of low birth weight, a three-fold increase in the risk of severe or life-threatening health conditions in newborns, and increased risks of pre-term birth and stillbirths.

The statistically insignificant change in cannabis intake during pregnancy might be due to more consistent messaging and efforts targeting pregnant people, which lacks for those in the preconception stage.

The results indicate that this means more messaging, education and public health interventions might be needed for cannabis users in the preconception stage, says Dr. Bayrampour.

“We don’t have or maintain a formal kind of preconception care in Canada, and it’s time we start thinking of the value of having this kind of care to ensure a great start for the pregnancy journey,” she said.

This study also compared the rates of alcohol, cigarette smoking and drug use before and after cannabis legalization. These rates remained mostly unchanged in both the preconception and during pregnancy.

Although most studies on cannabis look at pregnancy, these results lay the groundwork for future research to include the preconception stage, and people who may be chronic substance users.