In the United States, marijuana is the most used illicit drug during pregnancy and is a trend that is increasing. Recent estimates suggest that marijuana use complicates 2% to 5% of all pregnancies, and data from the Annual National Survey on Drug Use and Health revealed that since 2002, monthly marijuana use among pregnant women has increased by 62%. The actual number of marijuana-using mothers can only be determined by hair and other analyses, like we did to determine how many mothers smoked during their pregnancy.

As more medicinal claims are made without FDA study and approval, it should not surprise us that the number of women using marijuana during pregnancy or on a regular basis is increasing. Current data shows that 7.3% of Americans 12 or older regularly used marijuana in 2012, which is significantly higher than the 5.8% in 2007. Moreover, the majority of marijuana users are young and of reproductive age, and it is estimated that nearly half of female marijuana users continue to use the drug during their pregnancy. Even more troubling is that that the prevalence of regular cannabis use among the youngest and most socioeconomically disadvantaged women is three to four times higher than the national average, which adds another layer of risk to a population that is already overwhelmed by high-risk pregnancies and numerous health disparities.

Marijuana has not been studied as a medicine in clinical trials monitored by the FDA. FDA approval requires demonstration of the beneficial effects compared to placebo, utilizing prospective, double-blind methodology. In such a trial, women, including women of child-bearing age, would be protected by a lengthy process of study. Such a process has protected Americans since the thalidomide crisis in the 1950s.

Research About Marijuana and Pregnancy

Most existing research regarding marijuana use during pregnancy is retrospective. It took hundreds of studies before we could prove, via scientific methods, the risk and danger of alcohol consumption during pregnancy. Because of the research, we discovered fetal alcohol syndrome and a quantifiable spectrum of behavioral and neurological abnormalities in children exposed to ethanol in utero.

Today the best available evidence has identified a causal relationship between marijuana use and decreased birth weight, increased spontaneous abortion, impaired neurodevelopment, and functional deficits among children and adults who were exposed in utero. In addition, THC, the major psychoactive constituent of cannabis, has been identified in the breast milk of lactating woman who report only occasional cannabis use. Due to these adverse effects, the American College of Obstetricians and Gynecologists (ACOG) has alerted ob-gyns to “urge their patients who are pregnant or contemplating pregnancy to discontinue marijuana use” (2016).

What is not known is how cannabis (THC), at the molecular level, effects fetal development. This excellent paper by Friedrich, et al., offers new insights regarding the pharmacokinetic actions of THC and its impact on fetal environment and fetal development.

Why Does This Matter?

Due to its lipophilic nature, THC can easily cross the blood brain barrier and enter the placenta. In primate studies, THC was detectable in fetal blood 15 minutes after intravenous infusion in the mother. Three hours post-infusion, fetal THC blood levels matched maternal THC blood levels. Given the pharmacokinetic properties of THC, maternal blood can store THC for weeks, which results in prolonged fetal exposure. As a result, occasional use of marijuana during pregnancy, as little as once per month, results in fetal exposure that persists throughout the pregnancy.

Under stable conditions, cannabinoid 1 (CB1) signaling is involved in a number of critical processes necessary for healthy embryo attachment and development. Disruption of these critically important signaling pathways by marijuana exposure can result in numerous downstream deleterious effects, including:

  1. Embryotoxic effects on the uterine environment. Disruptions of cannabinoid signaling can cause irregularities in pre-implantation development, impede embryo transport to the uterus and compromise uterine receptivity during implantation.
  2. Decreased fetal folic acid (Vitamin B9) uptake. Folic acid is essential for healthy embryo development, particularly in the brain.
  3. Angiogenesis, cellular replication, tissue differentiation and impaired cognitive development are all associated with THC exposure in utero.

As use of cannabis continues to gain social acceptance, the need for better maternal prenatal education by medical providers, especially for higher risk populations, could prevent the adverse effects of marijuana on the developing child.