News Release 

Cannabis use disorder rate rose among pregnant women between 2001-2012

Study finds resulting adverse outcomes for infants: preterm births, low birth weight and small size

University of California - San Diego

Research News

A study of almost 5 million live births in California by researchers at the Herbert Wertheim School of Public Health and Human Longevity Science at University of California San Diego reports that babies born to mothers diagnosed with cannabis use disorder were more likely to experience negative health outcomes, such as preterm birth and low birth weight, than babies born to mothers without a cannabis use disorder diagnosis.

The findings are published online in the April 22, 2021 issue of the journal Addiction. The National Institute on Drug Abuse, part of the National Institutes of Health, funded the study.

Cannabis use disorder is a diagnostic term with specific criteria that defines continued cannabis use despite consequent, clinically significant impairments. The research team, led by first author Yuyan Shi, PhD, associate professor at The Herbert Wertheim School of Public Health, conducted a retrospective cohort study of 4.83 million mothers who delivered live, single births in California from 2001 to 2012.

They identified 20,237 women who were discharged after delivery with a diagnosis of cannabis use disorder. Not all people who use cannabis meet the criteria for cannabis use disorder. The study authors stated the actual incidence of cannabis use disorder is likely higher than reported numbers.

The researchers found that diagnoses of cannabis use disorder, based on medical records at time of delivery, rose from 2.8 to 6.9 per 1000 deliveries from 2002 to 2012. Compared to a matched control group of 40,474 mother-infant pairs, infants born to women with cannabis use disorder were more likely to be born preterm, have a low birth weight and be small for their gestational age -- all factors that can require greater or more intense medical care or presage later health issues.

Additionally, researchers found that, though rare overall (less than 1 percent), the risk of infant mortality was greater for infants born to women with cannabis use disorder. These infants were 35 percent more likely to die within a year of birth than infants in the control group. Conversely, these infants were also less likely to be hospitalized within the first year of life than control group infants.

"Because we are looking only at medical records, there is a lot we don't know about the mothers and infants in this study," said first author Shi, "but our analysis supports the recommendation that health professionals screen for and address cannabis use disorders in their pregnant clients -- to protect both their health and potentially the health of their infants."

Currently, screening for cannabis use or related disorders is not standard practice during pregnancy health care, though marijuana is the illicit drug most commonly used by pregnant women, typically to self-treat depression, anxiety, stress, pain, nausea and vomiting, often during the first trimester. It is also not standard of care to provide counsel on the lack of safety data around cannabis use during pregnancy. Both strategies may be helpful, as well as encouraging patients to discontinue use of cannabis during pregnancy and while breastfeeding and referring to treatment when appropriate.

According to a 2018 published study, approximately 7 percent of pregnant women self-reported marijuana use, with rates as high as 10 percent among women ages 18 to 25. Rates based on urine toxicology were even higher, with 19 percent of pregnant women ages 18 to 25 screening positive for marijuana use.

Previous research has found that tetrahydrocannabinol (THC), the psychoactive compound in cannabis, can reach fetuses and infants through the placenta and breastmilk, respectively. THC disrupts the normal function of the endocannabinoid system, which has been shown to play a key role in pregnancy, including implantation of the embryo in the uterus and maintenance of the placenta.

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Co-authors include: Bin Zhu, UC San Diego; and Di Liang, UC San Diego and Fudan University, China.

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