Newborn Health Harmed by Cannabis Exposure

Nancy A. Melville

February 19, 2019

In utero exposure to cannabis can lead to significantly higher rates of adverse outcomes, including low birth weight and preterm delivery, new research shows, and increasing numbers of pregnant women are using cannabis as legalization laws sweep the country.

"As marijuana has been legalized" in an increasing number of states, "become more potent, and gained acceptance, we have many women using it who do not necessarily engage in other negative health behaviors, such as tobacco, alcohol, and other drug use," said Beth Bailey, PhD, from the University of Colorado Denver Anschutz Medical Campus in Aurora.

"As a result, newer studies are identifying clear links between in utero marijuana exposure and adverse outcomes in exposed children," she said at the Society for Maternal-Fetal Medicine 2019 Annual Pregnancy Meeting in Las Vegas.

Bailey and her colleagues conducted a retrospective chart review of 1062 newborns delivered at one of six delivery hospitals in the University of Colorado Health System or one of five delivery hospitals in Tennessee and Virginia from July 2011 to June 2016.

In utero exposure to cannabis during late pregnancy was confirmed with a positive urine drug screen at delivery in 531 mothers of the newborns. The exposed infants were rigorously matched for background and other prenatal exposures with an equal number of control infants whose mothers had a negative drug screen.

Beth Bailey

The mean age of the mothers was 24 years and about three-quarters were white.

All birth outcomes examined were significantly worse for infants exposed to cannabis than for unexposed infants, after factors that could influence birth outcomes, such as mother's age, marital status, race, parity, socioeconomic status, and in utero exposure to tobacco, alcohol, benzodiazepines, and opioids, were controlled for (P < .05).

Cannabis-exposed newborns were 82% more likely than unexposed newborns to be of low birth weight, 79% more likely to be born before term, and 43% more likely to be admitted to the neonatal intensive care unit (NICU).

This is among the first relatively large and well-designed studies to show that birth outcomes are linked to cannabis exposure in pregnancy.

The fact that the worse outcomes were independent of other risk factors that are common with cannabis use, such as other drug exposure and sociodemographic risks, is notable, said Bailey.

"This is among the first relatively large and well-designed studies to show that birth outcomes are linked to cannabis exposure in pregnancy," said Katrina Mark, MD, from the University of Maryland School of Medicine in Baltimore.

The ability to see the effects independently sets this study apart from previous ones, Mark told Medscape Medical News. "There are plenty that show no differences linked to cannabis, but they are not usually as well designed as this one, and usually don't have as much correction for those confounding factors."

Another study, which identified alarming increases in the incidence of adverse obstetric outcomes after recreational cannabis use was legalized in Colorado in 2012, was presented at the meeting by Torri Metz, MD, from University of Utah Health in Salt Lake City.

Changes in Use, Outcomes After Legalization

Metz and her team looked at 2392 women who gave birth at the University of Colorado Denver, 1165 who delivered before legalization and 1227 who delivered after legalization.

Pregnant women were significantly more likely to use cannabis after legalization than before (odds ratio [OR], 1.8; 95% confidence interval [CI], 1.2 - 2.6; P = .01). In addition, after multivariate adjustment for factors such as ethnicity and other drug use, fetal growth restriction was more common after legalization (OR, 1.9; 95% CI, 1.2 - 2.9), as was spontaneous preterm birth (OR, 1.5; 95% CI, 1.1 - 2.0).

Other obstetrical outcomes evaluated were not significantly different between the two time periods.

Notably, there were no significant differences in the use of alcohol, tobacco, illegal drugs, or opioids between the two time periods.

These findings offer insight into the effect legalization might be having on women's impressions of cannabis use during pregnancy, Metz told Medscape Medical News.

The study was observational so, "at this point, this is simply an observed association and cannot be causally attributed to an increase in marijuana use. However, the finding warrants further investigation," she said.

Bailey and Metz have disclosed no relevant financial relationships.

Society for Maternal-Fetal Medicine (SMFM) 2019 Annual Pregnancy Meeting: Abstracts 75 and 341. Presented February 15 and February 13, 2019.

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