Drugs, Pregnancy & Lactation

Cannabis use in pregnancy and lactation: A changing landscape

Publish date: January 27, 2020

With recent developments in many U.S. states regarding legalization of cannabis for medicinal or recreational use, there is an emerging need to better understand the risks or safety of its use during pregnancy and lactation. National survey data from 2007-2012 of more than 93,000 pregnant women suggest that around 7% of pregnant respondents reported any cannabis use in the last 2-12 months; of those, 16% reported daily or almost daily use. Among pregnant past-year users in the same survey, 70% perceived slight or no risk of harm from cannabis use 1-2 times a week in pregnancy.¹

Dr. Christina D. Chambers

Data from the Kaiser Northern California health plan involving more than 279,000 pregnancies followed during 2009-2016 suggest that there has been a significant upward trend in use of cannabis during pregnancy, from 4% to 7%, as reported by the mother and/or identified by routine urine screening. The highest prevalence in that study was seen among 18- to 24-year-old pregnant women, increasing from 13% to 22% over the 7-year study period. Importantly, more than 50% of cannabis users in the sample were identified by toxicology screening alone.^2,3 Common reasons given for use of cannabis in pregnancy include anxiety, pain, and nausea and vomiting of pregnancy.⁴

With respect to adverse perinatal outcomes, several case-control studies have examined risks for major birth defects with maternal self-report of cannabis use. Some have noted very modest increased risks for selected major birth defects (odds ratios less than 2); however, data still are very limited.^5,6

A number of prospective studies have addressed risks of preterm birth and growth restriction, accounting for mother’s concomitant tobacco use.^7-11 Some of these studies have suggested about a twofold to threefold increased risk for preterm delivery and an increased risk for reduced birth weight – particularly with heavier or regular cannabis use – but study findings have not been entirely consistent.

Given its psychoactive properties, there has been high interest in understanding whether there are any short- or long-term neurodevelopmental effects on children prenatally exposed to cannabis. These outcomes have been studied in two small older cohorts in the United States and Canada and one more recent cohort in the Netherlands.^12-15 Deficits in several measures of cognition and behavior were noted in follow-up of those children from birth to adulthood. However, it is unclear to what extent these findings may have been influenced by heredity, environment, or other factors.

There have been limitations in almost all studies published to date, including small sample sizes, no biomarker validation of maternal report of dose and gestational timing of cannabis use, and lack of detailed data on common coexposures, such as alcohol, tobacco, and other drugs. In addition, newer studies of pregnancy outcomes in women who use currently available cannabis products are needed, given the substantial increase in the potency of cannabis used today, compared with that of 20 years ago. For example, the tetrahydrocannabinol (THC) concentration in commonly cultivated marijuana plants has increased threefold from 4% to 12% between 1995 and 2014.¹⁶

There are very limited data on the presence of cannabis in breast milk and the potential effects of exposure to THC and other metabolites for breastfed infants. However, two recent studies have demonstrated there are low but measurable levels of some cannabis metabolites in breast milk.^17-18 Further work is needed to determine if these metabolites accumulate in milk and if at a given dose and age of the breastfed infant, there are any growth, neurodevelopmental, or other clinically important adverse effects.

Related questions, such as potential differences in the effects of exposure during pregnancy or lactation based on the route of administration (edible vs. inhaled) and the use of cannabidiol (CBD) products, have not been studied.

At the present time, the American College of Obstetricians and Gynecologists recommends that women who are pregnant or contemplating pregnancy be encouraged to discontinue marijuana use. With respect to lactation and breastfeeding, ACOG concludes there are insufficient data to evaluate the effects on infants, and in the absence of such data, marijuana use is discouraged. Similarly, the American Academy of Pediatrics recommends women of childbearing age abstain from marijuana use while pregnant or breastfeeding because of potential adverse consequences to the fetus, infant, or child.

In August 2019, the U.S. Surgeon General issued an advisory regarding potential harm to developing brains from the use of marijuana during pregnancy and lactation. The Food and Drug Administration issued a similar statement in October 2019 strongly advising against the use of CBD, THC, and marijuana in any form during pregnancy or while breastfeeding.

Dr. Chambers is professor of pediatrics and director of clinical research at Rady Children’s Hospital and associate director of the Clinical and Translational Research Institute at the University of California, San Diego. She is also director of MotherToBaby California, president of the Organization of Teratology Information Specialists, and past president of the Teratology Society.