By Rebecca H. Allen, MD, MPH

Associate Professor, Department of Obstetrics and Gynecology, Warren Alpert Medical School of Brown University, Women and Infants Hospital, Providence, RI

Dr. Allen reports she is a Nexplanon trainer for Merck, and has served as a consultant for Bayer and Pharmanest.

SYNOPSIS: Marijuana use in pregnancy increased 62% from 2002 to 2014, especially among women 18-25 years of age.

SOURCE: Brown QL, Sarvet AL, Shmulewitz D, et al. Trends in marijuana use among pregnant and nonpregnant reproductive-aged women, 2002-2014. JAMA 2016; Dec.19. doi: 10.1001/jama.2016.17383 [Epub ahead of print].

This is a retrospective cohort study conducted using data from the United States National Survey on Drug Use and Health from 2002 to 2014. Sponsored by the Substance Abuse and Mental Health Services Administration, this is an annual nationwide survey involving interviews with approximately 70,000 randomly selected individuals aged 12 years and older across the United States. The participants privately enter their responses directly onto a laptop computer supplied by an in-person interviewer. Response rates have averaged 75% or higher since 2002. Lifetime use of marijuana or hashish was measured, as well as how recently the last use occurred (within the past 30 days, more than 30 days ago but within the past 12 months, or more than 12 months ago). Pregnant and non-pregnant women were compared by age (18-25 years and 26-44 years), and differences in trends over time were examined.

A total of 200,510 women were surveyed, with 29.5% aged 18-25 years and 70.5% aged 26-44 years. Of the total, 61.0% were white, 13.7% black, 17.2% Hispanic, and 8.1% other race/ethnicity. About 60% had some college education and 5.3% were pregnant. After controlling for age, race, income, and education, the adjusted prevalence of past-month marijuana use increased from 2.37% (95% confidence interval [CI],1.85%-3.04%) in 2002, to 3.85% (95% CI, 2.87%-5.18%) in 2014 (prevalence ratio [PR], 1.62; 95% CI, 1.09-2.43). The corresponding numbers for non-pregnant women were 6.29% (95% CI, 6.02%-6.57%) in 2002, to 9.27% (95% CI, 8.90%-9.65%) in 2014 (PR, 1.47; 95% CI, 1.38-1.58). The adjusted prevalence of past-month marijuana use was highest among those aged 18-25 years, reaching 7.47% (95% CI, 4.67%-11.93%) in 2014, significantly higher (P = 0.02) than among those aged 26-44 years (2.12%; 95% CI, 0.74%-6.09%).

COMMENTARY

Marijuana always has been the most common illicit drug used during pregnancy. With the growing number of states permitting medical marijuana and recreational marijuana use, we have started to see an increasing number of women using marijuana during pregnancy. Although the prevalence of past-month marijuana use among pregnant women overall in 2014 was only 3.85%, it was almost 7.5% among women aged 18-25 years. The methodology of the study permitted private answers to survey questions, which hopefully mitigated any social desirability bias. The concern in pregnancy is that women may turn to marijuana for the treatment of nausea and vomiting. In all states where medical marijuana is legal, nausea is a medically approved indication. One small study from Hawaii found that women who reported severe nausea during pregnancy were significantly more likely to report marijuana use during pregnancy (3.7% vs. 2.3%; PR = 1.63; 95% CI, 1.08-2.44).1 Given that most nausea and vomiting of pregnancy occurs in the first trimester, women are using this substance at a vulnerable period in fetal development.

Marijuana contains various cannabinoids, the main agent and the most commonly studied of which is tetrahydrocannabinol (THC). THC is known to cross the placenta and be present in breast milk.2 The effects of marijuana use in pregnancy are difficult to study because there are many confounding factors. Women who use marijuana also may smoke tobacco, use alcohol or other drugs, and have socioeconomic challenges that also can contribute to adverse pregnancy outcomes. As an example, one study of pregnant women found that marijuana users had lower levels of education, a lower household income, and were less likely to use folic acid supplements than non-users.3 In addition, most studies on marijuana use in pregnancy rely on self-reporting, which is vulnerable to bias. Also, the potency of marijuana and the concentration of THC will vary depending on the product used.

Although marijuana use is not thought to cause structural congenital malformations, it has been linked to negative effects on brain development.2 The fetal brain contains cannabinoid receptors, and endogenous cannabinoids play a role in brain development. Experiments in animals have shown a detrimental effect on normal brain development of exogenous THC. In humans, there is some evidence of effects on children in terms of impaired higher-order executive functions, such as visual-motor coordination, decreased attention span, and behavioral problems.4 Although there are limitations to the data on marijuana use in pregnancy, the American College of Obstetricians and Gynecologists recommends against use of marijuana during pregnancy.2 It certainly makes sense that if smoking tobacco should be avoided, then marijuana should be avoided as well. Women should be asked about marijuana use along with querying their use of tobacco, alcohol, and other drugs when presenting for prenatal care. Women who use marijuana should be counseled to stop using it during pregnancy. There are other, better-studied alternatives to treat nausea and vomiting. The healthcare and legal system also should allow for free reporting of substance use without women fearing civil or criminal penalties from disclosing use during their OB/GYN care. Clearly, more data are needed that can tease the effects of marijuana use during pregnancy so we can better understand and counsel women appropriately.

REFERENCES

  1. Roberson EK, Patrick WK, Hurwitz EL. Marijuana use and maternal experiences of severe nausea during pregnancy in Hawai‘i. Hawaii J Med Public Health 2014;73:283-287.
  2. American College of Obstetricians and Gynecologists Committee on Obstetric Practice. Committee opinion no. 637: Marijuana use during pregnancy and lactation. Obstet Gynecol 2015;126:234-238.
  3. van Gelder MM, Reefhuis J, Caton AR, et al. Characteristics of pregnant illicit drug users and associations between cannabis use and perinatal outcome in a population-based study. National Birth Defects Prevention Study. Drug Alcohol Depend 2010;109:243-247.
  4. Wu C-S, Jew CP, Lu H-C. Lasting impacts of prenatal cannabis exposure and the role of endogenous cannabinoids in the developing brain. Future Neurol 2011;6:459-480.