How much do we really know about marijuana use during pregnancy?
Department of Obstetrics and Gynecology, College of Physicians and Surgeons, Columbia University,
Department of Obstetrics and Gynecology, College of Physicians and Surgeons, and Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, USA
Mini commentary on ‘Cannabis use during pregnancy in France in 2010’
Marijuana is the most commonly used illicit recreational drug internationally (Copeland et al. Int Rev Psychiatry 2009;21:96–103). The Youth Risk Behavior Survey conducted by the US Centers for Disease Control and Prevention reported that 23.1% of high school students in the USA used marijuana in the past month, and that 39.9% had used marijuana at least once. Marijuana use is also not uncommon in Western Europe (MacArthur GJ et al. J Public Health 2012;34:i20–i30). Despite its ubiquitous prevalence, research on marijuana use in pregnancy remains limited. Although marijuana has been associated with reduced fetal growth and an increased risk of preterm delivery in some but not all studies, the use of the drug during pregnancy has generally not been associated with adverse pregnancy outcomes (Smith LM et al. Pediatrics 2006;118:1149–56; Shiono PH et al. Am J Obstet Gyn 1995;172:19–27). Few studies evaluating these outcomes are available, however.
The study by Saural-Cubizolles et al. is an important addition to the research literature on marijuana use in pregnancy. The authors analysed a national perinatal survey of women in France in 2010. Women were questioned regarding marijuana use during pregnancy, and drug use was evaluated in relation to adverse obstetric outcomes, including preterm delivery and small for gestational age, in a multivariate model. The main findings of the study are that marijuana use was associated with: (1) an increased risk of preterm birth; and (2) a lower mean birthweight. Both of these findings remained statistically significant within a multivariate model that included covariates such as age, smoking, parity, and employment status and income.
Do the risks shown in this study result from the study model being inadequately robust? Marijuana use may occur in a complex milieu of obstetric, medical, and social risk factors for adverse pregnancy outcomes. Methodological improvements that could improve the validity of future work include the following: (1) the use of biological tests to corroborate survey/interview responses; (2) a demonstration of a dose–response and/or temporal relationship between marijuana use and adverse obstetric outcomes; (3) the elucidation of mechanisms by which marijuana may cause preterm delivery and restricted fetal growth; (4) determining whether marijuana use is associated with greater smoking prevalence and, if so, whether exposure to both marijuana and smoking confer increased risks of adverse perinatal outcomes beyond the risks conferred by these substances independently; and (5) modelling the other risk factors for spontaneous and indicated preterm delivery, including detailed obstetric and medical history.
Legalised recreational marijuana use is gaining popularity and social acceptance, particularly in the USA, where taxes on the drug represent a new source of revenue. With increasing use, how harmful marijuana is in pregnancy will dictate whether it becomes an obstetrical public health concern akin to alcohol and tobacco. Although marijuana use in pregnancy should of course be discouraged, more data are needed to determine what public health resources should be used to screen for, counsel, and educate patients about the drug's potential obstetric risks. High-quality evidence is the best basis for these important forthcoming public policy decisions.
Disclosure of interests
C.A. is the Editor-in-Chief of Paediatric and Perinatal Epidemiology, an international journal that is also published by Wiley-Blackwell.