What to Tell Pregnant Women About Marijuana

Jennifer Gunter, MD


June 20, 2017

I was surprised to read in a recent New York Times article, "A Balm When You Are Expecting: Sometimes Pot Does the Trick," that almost half of the women who contacted the paper about their marijuana use during pregnancy felt that there were few, if any, risks.[1]

Science, too, tells us that the use of marijuana by pregnant women is increasing. In 2014, for example, 3.9% of pregnant women between the ages of 18 and 44 years reported marijuana use in the past month versus 2.4% in 2002.[2] The reasons behind the increased use of marijuana in pregnancy are not fully known. More women may be using marijuana recreationally given increasing legalization, others may use marijuana for medical reasons prepregnancy and choose to continue, while others may use it to manage pregnancy nausea. In one study, women with severe nausea were significantly more likely to use marijuana in pregnancy versus those without severe nausea (3.7% vs 2.3%, respectively).[3]

Health Effects

Botanical marijuana, Cannabis sativa, contains over 60 pharmacologically active cannabinoids.[4] Both tetrahydrocannabinol (THC), the main psychoactive ingredient, and cannabidiol (CBD) may help nausea; and CBD may help some types of pain and spasticity.[4,5,6,7] After inhalation, THC concentrations rise rapidly in the blood stream, and even a single inhalation of a low-dose marijuana cigarette (16 mg THC) produces measurable levels of THC.[7,8] THC is highly lipophilic, so chronic smokers have significantly higher levels of THC after smoking as compared with infrequent users given the extended excretion from fatty tissue.[7,9] Because marijuana clears slowly from both maternal and fetal fat, fetal exposure to THC continues even after a mom stops using it.[7] Cannabinoids readily cross the placenta, entering the fetal circulation and brain, and higher fetal levels are seen with chronic use.[7,8,9,10,11,12]

Another concern is that doses of THC in marijuana have increased dramatically, from 4% in 1995 to 12% in 2014, with labs in Colorado reporting THC concentrations in some strains as high as 30%.[13] Women choosing to use marijuana in pregnancy will be exposed to significantly higher doses compared with 20 years ago.[5,13] And many strains that claim to be high in CBD in fact contain little, if any.[13] While women may think that marijuana concentrates and edibles are healthier because they do not involve smoking, they can still have significant and potentially harmful solvent residue from processing with chemicals such as butane.[13]

The endocannabinoid system is complex and not fully understood. In pregnancy it is involved from fertilization to implantation and placentation as well as in parturition.[7,14] In vitro studies with cannabinoid exposure indicted disruption of cellular messaging, angiogenesis, premature cellular death, and decreased folic acid uptake by cells.[5,14]

THC affects the CB1 receptor, which has an important regulatory role in brain development.[11,15] Animal studies show that prenatal exposure to THC, even at low doses, causes long-lasting neurologic changes among exposed progeny.[15] A recent meta-analysis of 24 studies of sufficient quality indicates that women who use cannabis during pregnancy have an increased risk for anemia and that fetal exposure reduces birth weight and increases the need for neonatal intensive care unit admission.[16]

What to Do About It

The American College of Obstetricians and Gynecologists (ACOG) recommends asking all women about marijuana use. Given the unsubstantiated reports of safety that women may find online, prenatal providers should be prepared to provide clear information about the safety concerns in a nonjudgmental way. It's important that women get this information from their health providers so that they have accurate data to inform their medical decision-making. Prenatal providers should encourage women to report nausea and vomiting early and not downplay symptoms, as lack of help from traditional medicine may be one reason that women turn to marijuana. Providers should know that ACOG specifically recommends against advising marijuana use for nausea and vomiting in pregnancy.[11] ACOG also recommends that providers help women who are using marijuana for medical reasons to find alternatives with pregnancy safety data.[11]

Discussions about marijuana can be hard as the "safety" of the drug seems entrenched. But I've found that many patients are receptive when I explain to them the extremely high concentrations of THC in modern strains, the often low levels of CBD despite advertising to the contrary, and concerns about solvents.


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