With many states now considering the legalization of medical marijuana, there seems to be a growing sense that marijuana is relatively safe and may, in some cases, be more attractive or effective than traditional pharmacologic interventions.  We have witnessed this shift in attitude in our clinic, where many of our clinicians have been surprised to hear women ask questions about the dangers of using antidepressants and other medications during pregnancy while at the same time feeling relatively comfortable with their use of marijuana in the same setting.

So is it safe to use marijuana if you are pregnant or planning to conceive? This is an especially important question as the use of marijuana in the United States appears to be increasing.  According to a nationwide survey, 7.3% of Americans 12 or older regularly used marijuana in 2012, up from 5.8% of Americans in 2007.  The majority of these users are young and of reproductive age.

At this point, our data regarding the reproductive safety of marijuana is fairly limited.  This data may be particularly hard to gather, as self-report of use is often unreliable, especially in areas where the use of marijuana is illegal.

In a recent study, Marroun and colleagues examined the relationship between maternal cannabis use and fetal growth in a population-based sample of 7,452 mothers with singleton pregnancies.  The results indicated that using cannabis before pregnancy did not affect fetal growth.  However, maternal cannabis use during pregnancy was associated with growth restriction in mid-and late pregnancy and was also associated with lower birth weight.  Growth restriction was most pronounced for those with continued use throughout pregnancy.

Another study suggests that cannabis use during pregnancy, either alone or in combination with smoking and exposure to second-hand smoke, was associated with an increased risk of stillbirth.  This was a case-control conducted by the Stillbirth Collaborative and attempted to include all stillbirths and representative liveborn controls. Rather than relying solely on self-reporting, this study collected and analyzed umbilical cord samples from cases and controls for illicit drugs. Maternal serum was also assayed for cotinine, a metabolite of nicotine which is used as a biomarker for exposure to tobacco smoke.

In this study a positive cord test for any illicit drug was associated with about a twofold increase in risk of stillbirth (odds ratio [OR] 1.94). The most common individual drug was cannabis (OR 2.34), although some of this effect may have been caused by smoking tobacco. Both maternal self-reported smoking history and maternal serum cotinine levels were associated in a dose-response relationship with stillbirth. Positive serum cotinine levels of less than 3 ng/mL and no reported history of smoking (consistent with passive smoke exposure) were also associated with stillbirth (OR 2.06, 95% CI 1.24-3.41).

Other studies have attempted to measure the consequences of prenatal marijuana use in terms of its effects on the behavioral and cognitive development of the exposed children.  There is increasing evidence that the developing brain in exquisitely vulnerable.

Goldshmidt and colleagues found there was a significant nonlinear relationship between marijuana exposure and child intelligence. Heavy marijuana use (one or more cigarettes per day) during the first trimester was associated with lower verbal reasoning scores on the Stanford-Binet Intelligence Scale.  Other studies have demonstrated that prenatal marijuana exposure is associated with memory problems, executive functioning deficits, and higher rates of depression and anxiety.

Our information regarding the effects of marijuana on the developing fetus remains limited; however, the data we do have suggests that there may be some negative effects on fetal growth and development.

Ruta Nonacs, MD PhD

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