Marijuana Use in Pregnancy and While Breastfeeding

Abstract

The prevalence and perceived safety of marijuana use in pregnancy are increasing with expanding legalization. Marijuana crosses the placenta and passes into breast milk, resulting in fetal and neonatal exposure. Many women cite medical reasons for prenatal marijuana use such as nausea and vomiting of pregnancy, anxiety, and chronic pain. The scientific literature regarding marijuana in pregnancy is mixed, resulting in confusion among practitioners as to how to counsel women about risks of use. In addition, there is a paucity of literature related to marijuana use and breastfeeding. Existing pregnancy studies are predominantly retrospective cohorts with a reliance on self-report for ascertainment of exposure, which underestimates use. Many studies fail to adjust for important confounding factors such as tobacco use and sociodemographic differences. Despite the limitations of the existing evidence, there are animal and human data suggesting potential harm of cannabis use. The harms are biologically plausible given the role of the endocannabinoid system in pregnancy implantation, placentation, and fetal neurologic development. Two recent systematic reviews and meta-analyses found an association between marijuana use and adverse perinatal outcomes, especially with heavy marijuana use. In addition, three longitudinal cohort studies demonstrate a possible effect of prenatal marijuana exposure on long-term neurobehavioral outcomes. Marijuana use may be associated with growth restriction, stillbirth, spontaneous preterm birth, and neonatal intensive care unit admission. Therefore, women should be advised to refrain from using marijuana during pregnancy and lactation.

Figure 1

After consumption, the primary psychoactive component of marijuana, delta-9-tetrahydrocannabinol, undergoes various absorption, metabolism, and excretion pathways based on method of administration. Illustration of the human liver anatomy © Erhan Akin, Dreamstime.com. Used with permission.

Figure 2

This is a schematic representation of endocannabinoid signaling at the site of implantation and potential adverse effects. Physiologic and molecular processes involving anandamide (AEA) are normally tightly regulated by N-acylphosphatidylethanolamine-specific phospholipase D (NAPE-PLD) and fatty acid amide hydrolase (FAAH) for synthesis and degradation, respectively. Disruption of endocannabinoid signaling (shown in yellow boxes) can result in reprogramming of cellular function at the implantation site. Reprinted under the Creative Commons Attribution License from Fonseca BM, Correia-da-Silva G, Almada M, Costa MA, and Teixeria NA. The endocannabinoid system in the postimplantation period: a role during decidualization and placentation. Int J Endocrinol 2013;2013:510540. http://dx.doi.org/10.1155/2013/510540.

Figure 3

Graphical representation of results from two recent meta-analyses evaluating the effect of prenatal marijuana use on maternal and neonatal outcomes. Pooled adjusted estimates are based on a pooling of adjusted estimates from individual studies which all adjusted for tobacco, some also adjusted for other illicit drugs and other sociodemographic factors. A. Pooled odds ratios and relative risks for adverse perinatal outcomes with prenatal marijuana exposure. B. Pooled difference in gestational age at delivery in weeks associated with marijuana exposure. C. Pooled difference in birthweight (grams) of newborns associated with marijuana exposure. D. Pooled difference in neonatal length (cm) associated with marijuana exposure. E. Pooled difference in head circumference (cm) associated with marijuana exposure. pRR, pooled relative risk; pOR, pooled odds ratio; apRR; adjusted pooled relative risk; NICU, neonatal intensive care unit.

Figure 4

Mean concentration-time profile of delta-9-tetrahydrocannabinol in human milk (mean±standard deviation, n=8). Reprinted from Baker T, Datta P, Rewers-Felkins, K, Thompson, H, Kallem RR, Hale TW. Transfer of inhaled cannabis into human breast milk. Obstet Gynecol 2018;131:783–788.

Figure 5

Tabular representation of the Colorado Department of Public Health and Environment Retail Marijuana Public Health Advisory Committee Summary of Available Scientific Evidence. Substantial evidence was robust findings that support an association. Moderate evidence was findings support an association but with some limitations. Limited evidence was modest findings support an association but with substantial limitations. Insufficient evidence was not enough studies to conclude whether or not there is an association. Mixed evidence was defined as both supporting and non-supporting findings for an association with neither direction dominating. Reprinted with permission from the Colorado Department of Public Health and Environment. Environment’s Monitoring Health Concerns Related to Marijuana in Colorado: 2016 Report, Pregnancy and Breastfeeding evidence summary table.