Mothers who use cannabis during pregnancy risk disrupting immune gene networks in the placenta and potentially increasing the risk of anxiety and hyperactivity in their children.
Dr. Yasmin Hurd
These findings emerged from a study led by Yasmin Hurd, PhD, a professor of psychiatry and director of the Addiction Institute at the Icahn School of Medicine at Mount Sinai, New York, and Yoko Nomura, PhD, a professor of behavioral neuroscience at Queen’s College, City University of New York, that was published online in Proceedings of the National Academy of Sciences.
The analysis assessed the effects of gestational maternal cannabis use on psychosocial and physiological measures in young children as well as its potentially immunomodulatory effect on the in utero environment as reflected in the placental transcriptome.
Participants were drawn from a larger cohort in a study launched in 2012; the investigators evaluated offspring aged 3-6 years for hair hormone levels, neurobehavioral traits on the Behavioral Assessment System for Children survey, and heart rate variability (HRV) at rest and during auditory startle.
Dr. Yoko Nomura
The cohort consisted of 322 mother-child dyads and children with prenatal exposure to cannabis were compared with those having no exposure. The cohort consisted of 251 non–cannabis-using mothers and 71 cannabis-using mothers, with mean maternal ages in the two groups of 28.46 years and 25.91 years, respectively, The mothers gave birth at Mount Sinai and they and their children were assessed annually at affiliated medical centers in Mount Sinai’s catchment area.
For a subset of children with behavioral assessments, placental specimens collected at birth were processed for RNA sequencing.
Among the findings:
- Maternal cannabis use was associated with reduced maternal and paternal age, more single-mother pregnancies, state anxiety, trait anxiety, depression, cigarette smoking, and African American race.
- Hair hormone analysis revealed increased cortisol levels in the children of cannabis-using mothers, and was associated with greater anxiety, aggression, and hyperactivity.
- Affected children showed a reduction in the high-frequency component of HRV at baseline, reflecting reduced vagal tone.
- In the placenta, there was reduced expression of many genes involved in immune system function. These included genes for type I interferon, neutrophil, and cytokine-signaling pathways.
Several of these genes organized into coexpression networks that correlated with child anxiety and hyperactivity.
The principal active component of cannabis, tetrahydrocannabinol (THC), targets the endocannabinoid system in placental tissue and the developing brain, the authors noted. Exposure during pregnancy is associated with a range of adverse outcomes from fetal growth restriction to low birth weight and preterm birth.
“There are cannabinoid receptors on immune cells, and it is known that cannabinoids can alter immune function, which is important for maintaining maternal tolerance and protecting the fetus,” Dr. Hurd said. “It’s not surprising that something that affects the immune cells can have an impact on the developing fetus.”
“Overall, our findings reveal a relationship between [maternal cannabis use] and immune response gene networks in the placenta as a potential mediator of risk for anxiety-related problems in early childhood,” Dr. Hurd and colleagues wrote, adding that the results have significant implications for defining mental health issues in the children gestated by cannabis-smoking mothers.
Their results align with previous research indicating a greater risk for psychiatric illness in children with prenatal cannabis exposure from maternal use.
“While data are pretty limited in this realm, there are other studies that demonstrate a relationship between early child developmental and behavioral measures and cannabis use during pregnancy,” Camille Hoffman, MD, MSc, a high-risk obstetrics specialist and an associate professor at the University of Colorado at Denver, Aurora, said in an interview. “Our research group found children exposed to cannabis in utero at 10 weeks’ gestation and beyond were less interactive and more withdrawn than children who were not exposed.”
And THC remains in maternal breast milk even 6 weeks after usage stops.
The long-term effects of prenatal cannabis exposure remain to be determined and it is unknown whether the effects of gestational THC might attenuate as a child grows older. “We use early childhood measures in research as a proxy for the later development of diagnosed mental health conditions or behavioral problems,” Dr. Hoffman explained. “We know when we do this that not every child with an abnormal score early will go on to develop an actual condition. Fortunately, or unfortunately, other factors and exposures during childhood can change the trajectory for the better or worse.”
According to Dr. Hurd, child development is a dynamic process and epigenetic events in utero need not be deterministic. “The important thing is to identify children at risk early and to be able to go in and try to improve the environment they’re being raised in – not in terms of impoverishment but in terms of positive nurturing and giving the mother and family support.”
At the prenatal level, what’s the best advice for cannabis-using mothers-to-be? “If a woman doesn’t know she’s pregnant and has been using cannabis, taking extra choline for the remainder of the pregnancy can help buffer the potential negative impact of the cannabis exposure,” Dr. Hoffman said. The Food and Drug Administration and the American Medical Association recommend a dose of 550 mg daily. “The same is true for alcohol, which we know is also very bad for fetal brain development. This is not to say go ahead and use these substances and just take choline. The choline is more to try and salvage damage to the fetal brain that may have already occurred.”
This study was supported by the National Institute of Mental Health and the National Institute on Drug Abuse. The authors declared no competing interests. Dr. Hoffman disclosed no conflicts of interest with respect to her comments.