Conference Coverage

How to counsel women about marijuana in pregnancy



Physicians are by and large doing “pretty poorly” at counseling women about the use of marijuana during pregnancy, Torri D. Metz, MD, observed at the annual meeting of the Teratology Society.

This is of particular concern because the increasing legalization of recreational marijuana across the United States means growing use, possibly including use by pregnant women. National surveys indicate a high percentage of pregnant women believe there is slight or no harm in using marijuana once or twice per week, said Dr. Metz, an ob.gyn. at the University of Colorado, Denver, who is researching the effects of marijuana in pregnancy.

Dr. Torri D. Metz, University of Colorado, Denver Bruce Jancin/Frontline Medical News

Dr. Torri D. Metz

As an ob.gyn. practicing in Colorado – one of the first states to legalize recreational marijuana and a state where medical marijuana is protected under the state constitution – Dr. Metz often fields questions from obstetric care providers frustrated by patients who say, “I’m going to use it. You can’t show me data that says it’s not safe.”

Here’s how she likes to handle that situation: She starts out by freely admitting that that’s true. The available evidence is limited, mixed, and often flawed.

“I say, ‘I can’t give you data that says absolutely it’s not safe, but I also absolutely cannot give you data saying it is safe.’ I would favor saying, ‘I can’t tell you it’s safe. And if there’s any possible risk, let’s talk about things we know are safe we can use as alternatives for whatever you’re using cannabis for,’ ” she explained.

A Colorado survey of more than 1,700 mothers in the WIC (Women, Infants, and Children) nutrition program shed light on the reasons women use marijuana while pregnant or breastfeeding. Sixty-three percent of current users cited as a perceived benefit that it helped with depression, anxiety, and/or stress. Sixty percent reported it helped with pain. Nearly half used marijuana for nausea and vomiting. Just 39% did so for recreation.

Dr. Metz’s anecdotal experience has been that many health care providers are flubbing the opportunity to counsel women about marijuana use in pregnancy. This impression was bolstered by a recent study by investigators at the University of Pittsburgh who audio-recorded 468 first prenatal visits.

In total, 19% of patients disclosed marijuana use to 47 health care providers. In nearly half of those encounters, the providers didn’t respond to the disclosure at all. And when they did respond, it typically wasn’t by providing thoughtful, informed counseling on the risks or outcomes of using marijuana in pregnancy. Instead, the response was most often punitive: for example, a warning that evidence of use at delivery would result in a call to child protective services (Obstet Gynecol. 2016 Apr;127[4]:681-7).

Because of Colorado’s lengthy experience with legalized marijuana, the state Department of Public Health and Environment has endeavored to create resources of value for health care providers and patients ( The website contains a fact sheet for patients regarding marijuana in pregnancy and breastfeeding. For physicians, there is plain-language guidance on how to talk effectively about marijuana with patients, including suggested responses to selected commonly voiced misconceptions.

The website also includes the results of a 2014 marijuana-in-pregnancy literature review by a state advisory committee composed of Colorado specialists in pediatrics, ob.gyn., family medicine, public health, and addiction medicine.

The committee determined that there is moderate evidence that the use of marijuana in pregnancy is associated with increased risk of reduced fetal growth, lower IQ scores in young children, adverse effects on a child’s cognitive function and academic ability, and an increase in attention problems. There was deemed to be limited evidence of an association with stillbirth and isolated ventricular septal defects. There is also “mixed” evidence for associations with preterm delivery, reduced birth weight, and selected congenital anomalies.

Since that 2014 review, a new signal of potential harm stemming from maternal marijuana use in pregnancy has appeared: a possible increased risk of neonatal ICU admission. In one retrospective study including 361 marijuana users and 6,107 nonusers, the users had a 1.54-fold increased risk for neonatal ICU admission in an analysis adjusted for maternal demographics and tobacco use (J Perinatol. 2015 Dec;35[12]:991-5).

Moreover, investigators at the University of Arizona in Tucson performed a meta-analysis of 24 studies and concluded that infants exposed to cannabis in utero were at 2.02-fold increased likelihood of neonatal ICU admission, a 1.77-fold increased risk of low birth weight, and 1.36-fold increased odds of anemia (BMJ Open. 2016 Apr 5;6[4]:e0009986. doi: 10.1136/bmjopen-2015-009986).

“That obviously would have a big public health impact,” Dr. Metz said.

In marked contrast, however, just a few months later investigators at Washington University in St. Louis reported finding no significantly increased risk of neonatal ICU admission or any other adverse neonatal outcome after adjustment for tobacco use and other potential confounders in a meta-analysis of 31 studies (Obstet Gynecol. 2016 Oct;128[4]:713-23).

These contradictory meta-analyses underscore a key point about the existing literature on the safety of marijuana use in pregnancy: It provides few, if any, definitive answers. The studies conducted in the 1980s and 1990s are of limited generalizability because concentrations of tetrahydrocannabinol were so small, compared with today’s products. Ascertainment of exposure to marijuana in pregnancy is unreliable in the absence of confirmatory biologic sampling. Self-reported use is unreliable and is typically an underestimate. Adjustment for confounders associated with adverse neonatal outcomes is challenging.

“Biologic sampling is critical,” Dr. Metz said. “We actually don’t know who’s using, and we lack information on the timing and quantity of exposure.

“Part of the problem is the data are so mixed that you can really find whatever you want in the literature to support your bias,” she added.

Still, in light of the signals of possible harm, she urged her colleagues to advise patients not to use marijuana in pregnancy. Patients need to understand that there are no known benefits of marijuana use in pregnancy, there are possible risks, and there is no known safe amount of cannabis in pregnancy.

Dr. Metz reported having no financial conflicts related to her presentation.

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