Prenatal cannabis exposure may increase pregnancy risks

Exposure to cannabis prenatally was associated with adverse maternal and neonatal outcomes, according to a Canadian cohort study published in PLOS ONE.

“With the legalization of cannabis in Canada, it was critical for us to understand the potential impact of use in pregnancy,” Sabrina Luke, PhD, an epidemiologist at Perinatal Services British Columbia of the Provincial Health Services Authority in Vancouver, British Columbia, told Healio. “While Canada has long engaged in the routine surveillance of alcohol and tobacco, there is currently no standardized national surveillance of cannabis use in pregnancy.”

Luke and colleagues analyzed data from 1,280,447 singleton births between April 2012 and March 2019 reported in British Columbia’s Perinatal Data Registry, the Better Outcomes Registry & Network Ontario and the Perinatal Program Newfoundland and Labrador.

The researchers evaluated pregnancy risks associated with maternally self-reported cannabis use documented by providers at antenatal visits and hospital admission for delivery. Specifically, they calculated the risks for low birth weight, small and large for gestational age, spontaneous and medically indicated preterm birth, very preterm birth, stillbirth, major congenital anomalies — such as neural tube defects, orofacial clefts and limb deficiency defects — cesarean delivery, gestational diabetes and gestational hypertension.

Across the study period, the prevalence of cannabis use was 2%, increasing from 1.5% in the 2012 to 2013 fiscal year to 2.5% in the 2018 to 2019 fiscal year. Cannabis users were more likely to be younger, overweight or obese, co-use other substances, live in a rural area and in a neighborhood within the lowest income quintile compared with nonusers.

Compared with pregnant people who did not use cannabis, those who did had greater odds of:

• preterm birth (adjusted OR = 1.85; 95% CI, 1.74-1.94);
• spontaneous preterm birth (aOR = 1.8; 95% CI, 1.68-1.93);
• medically indicated preterm birth (aOR = 1.94; 95% CI, 1.77-2.12);
• very preterm birth (aOR = 1.73; 95% CI, 1.48-2.02);
• low birth weight (aOR = 1.9; 95% CI, 1.79-2.03);
• small for gestational age (aOR = 1.21; 95% CI, 1.16-1.27);
• large for gestational age (aOR = 1.06; 95% CI, 1.01-1.12);
• any major congenital anomaly (aOR = 1.71; 95% CI, 1.49-1.97);
• cesarean section (aOR = 1.13; 95% CI, 1.09-1.17); and
• gestational diabetes (aOR = 1.32; 95% CI, 1.23-1.42).

There was no association between cannabis use and stillbirth or gestational hypertension.

Of note, there were sex differences in the risks for small for gestational age and spontaneous preterm birth associated with cannabis use.

“We were surprised to find that female infants may be more susceptible to the effects of cannabis use in pregnancy,” Luke said.

Moving forward, clinicians should use these findings to counsel patients on cannabis use during pregnancy using a “trauma-informed, culturally safe, harm reduction approach,” Luke said.

Future research should expand knowledge of the effects of cannabis use on infants while breastfeeding, as well as the impact of prenatal use on the long-term health of children, Luke added.