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Cannabis during pregnancy increases maternal anaemia, causes adverse neonatal outcomes

Kavitha G.Shekar
04 May 2016

Cannabis use during pregnancy increases the risk of maternal anaemia, and causes several adverse outcomes in infants like low birth weight (LBW), and increased neonatal intensive care unit (NICU) admissions, show findings of a systematic review and meta-analysis.

Why focus on cannabis?

This study comes at a time when the global trend of cannabis use and social acceptance is increasing. [BMJ Open 2016;doi:10.1136/bmjopen-2015-009986]

High rate of cannabis use has been reported in West and Central Africa (12.4 percent), North America (12.1 percent), Colombia (15.2 percent), and Oceania (10.8 percent). [Crime, U.N.O.o.D.a. World drug report.http://www.unodc.org/documentslwdr2014/World_Drug_Report_2014_web.pdf]

As more countries begin to legalize this drug, the authors call for an increase in education and awareness of the harmful side-effects cannabis has on pregnancy.

“Pregnant women could benefit from health education on the potential adverse effects of the use of cannabis during pregnancy,” said author Professor John Ehiri from the Department of Health Promotion Sciences, Mel and Enid Zuckerman College of Public Health, University of Arizona, Tucson, Arizona, US. “As use of cannabis continues to become socially acceptable in many countries, understanding the effects of maternal and foetal health should become global priority.”

Cannabis and anaemia in pregnant women

Cannabis use increased the odds of anaemia in pregnant women compared to non-users (pooled odds ratio [pOR], 1.36, 95 percent confidence interval [CI], 1.10-1.69). The association of anaemia and pregnancy was reported in six studies. [Neurobehav Toxico/ Teratol 1982;4:447-450; Acta Med Iran 2012;50:411-416; BJOG 2002;109:1148-1153; Subst Use Misuse 1996;31:1063-1076; Drug Alcohol Depend 1983;11:359-66]

One of the studies reported increased odds of having a labour last more than 3 hours in mothers who used cannabis. [Neurobehav Toxico/ Teratol 1982;4:447-450]

Adverse effects on infants exposed to cannabis

Foetal weight decreased by 109.42g when they were exposed to cannabis in utero (95 percent CI, 38.72-180.12). LBW (<2,500g) among infants of cannabis users was reported in several studies (pOR, 1.77, 95 percent CI, 1.04-3.01). [Neurobehav Toxicol Teratol 1982;4:447-450; Int J Environ Res Public Health 2014;11:4991-5005; Pediatr Res 2012;71:215-219; Pediatrics 1997;100:79-83; Am J Perinato 1990;7:36-38; Subst Use Misuse 1996;31:1063-1076; Drug Alcohol Depend 1983;11:359-366]

A significant reduction in gestational length was also reported in users of cannabis (95 percent CI, -0.65-0.45). Infant head circumference was also decreased when they were exposed to this drug.

Infants exposed to cannabis also had higher odds of NICU stay compared to those who were not (pOR, 2.02, 95 percent CI, 1.27-3.21).

The inner aorta was significantly smaller in diameter, and pulmonary peak systolic velocity was lower in foetuses whose mothers who used cannabis throughout pregnancy. [Early Hum Dev 2010;86:231-236].

Ehiri and team conducted a systematic review of PubMed/MEDLINE, Ovid/MEDLINE, CINAHL/EBSCO, Psychinfo/EBSCO, Web of Science, Sociological Abstracts and EMBASE databases from inception until April 2014. They included 24 studies of pregnant women who used cannabis during pregnancy and infants who experienced exposure in utero.

“The data summarized [in this study] may be useful in guiding policy, practice, and future research on the benefits and harms associated with use of cannabis during pregnancy,” said Ehiri adding that more research in this area with sole focus on the harmful maternal and foetal effects of cannabis is required. 

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