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Marijuana in pregnancy linked to low birth weight

70% of women believe there is minimal harm

Jo Carlowe

Tuesday, 03 December 2019

Daily marijuana use during pregnancy may lead to a range of negative foetal outcomes, new research* shows.

In the latest issue of the Journal of Maternal-Fetal and Neonatal Medicine, physicians reviewed sonogram data from nearly 450 pregnant women who self-reported daily marijuana use. They found that daily cannabis use is associated with delayed foetal growth, which can put a baby at risk of certain health problems during pregnancy, delivery, and even after birth.

These problems include low birth weight, hypoglycaemia, low Apgar scores, among others, and in the most severe cases, delayed growth leading to stillbirth.

Physicians also found an increase in placental vascular resistance in both the second and third trimesters.

"Recent data from JAMA (The Journal of the American Medical Association) indicates that marijuana use in pregnancy has doubled over the last 15 years and what's more alarming is that 70% of women believe there is minimal or no harm from using marijuana in pregnancy," said Dr Bobby Brar, of the University of Nevada, Las Vegas (UNLV) School of Medicine Resident Physician and a lead author of the study. "Our findings contribute to the growing body of evidence that foetal marijuana exposure may not be as safe as people think.”

The physicians noted that the exposure to some chemical compounds that can be found in both tobacco and marijuana smoke may explain the growth abnormalities they observed. The compounds, known as polycyclic aromatic hydrocarbons, are present in both tobacco and marijuana smoke, but some studies have shown a higher concentration of these substances in second-hand marijuana smoke when compared to tobacco smoke, the physicians wrote.

It's likely that the exposure to the smoke, and not necessarily nicotine, which is found in tobacco, or THC (
Tetrahydrocannabinol), which is found in marijuana, is what leads to delayed foetal growth, the authors wrote.

While additional studies are needed to further understand the negative impacts of daily marijuana usage on foetal growth, the team of doctors said that cannabis use should be discouraged during pregnancy.

The physicians embarked upon the research as recent legalisation of marijuana across the USA has increased overall use. Current reports estimate that about 16% of pregnant women (in America) engage in daily use.

Additionally, the researchers argue that patients should be screened throughout pregnancy for marijuana use and counselled appropriately on its potential effects, as well as strategies for cessation.


*Brar BK, Patil PS, Jackson DN, et al. Effect of intrauterine marijuana exposure on fetal growth patterns and placental vascular resistance. Journal of Maternal-Fetal and Neonatal Medicine. Published online: 11 Nov 2019. DOI: 10.1080/14767058.2019.1683541

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