THC During Pregnancy Affects Fetal Development

Researchers at Oregon Health & Science University discovered that taking THC while pregnant could impair fetal development and have long-term health consequences for offspring.

The preclinical study was published today in the journal Clinical Epigenetics.

THC, or delta-9-tetrahydrocannabinol, is the primary psychoactive element in cannabis, a narcotic that is gaining popularity and availability in the United States. Cannabis usage during pregnancy is also on the rise, particularly during the first trimester, when the fetus is most exposed to environmental exposures, to alleviate common symptoms such as morning sickness. However, the possible consequences of prenatal cannabis usage on fetal development remain ambiguous, owing in part to a paucity of safety data. The purpose of this study was to determine the long-term health effects of THC consumption during pregnancy.

OHSU researchers discovered that exposing a pregnant person to THC affected the placental and fetal epigenome — including the chemical alterations to DNA responsible for gene regulation and expression, or telling genes what, where, and when to do something. Researchers discovered that these changes in gene regulation and expression are consistent with those reported in several common neurobehavioral disorders, including autism spectrum disorder.

“Cannabis is one of the most commonly used drugs and is widely available across the country, so there is a common perception that its completely safe to use,” said the study’s lead author Lyndsey Shorey-Kendrick, Ph.D., a computational biologist in the Division of Neurosciences at OHSU’s Oregon National Primate Research Center, or ONPRC. “The reality is that cannabis still carries many health risks for certain populations, including those who are pregnant. If we’re able to better understand the impacts, we can more effectively communicate the risks to patients and support safer habits during the vulnerable prenatal period.”

In a nonhuman monkey model, researchers provided THC in the form of a daily consumable and compared its effects to those of a placebo group. Researchers examined epigenetic alterations in numerous important sites that suggest good prenatal development, including the placenta — the disc of tissue that joins the umbilical cord and the uterus — as well as the fetal lung, brain, and heart.

Analyses revealed that THC exposure affected the epigenome, which is a mechanism by which the information contained in a gene is converted into a function or observable trait. Because genes — the segments of DNA that make up DNA — are all specifically coded to contribute to distinct functions of the body and brain, any impact on epigenetic processes caused by drug exposure is problematic, especially during a critical developmental window like pregnancy.

Significant alterations were discovered in genes linked to prevalent neurobehavioral diseases such as autism spectrum disorder and attention deficit hyperactivity disorder. These problems have been associated to poorer memory and verbal reasoning skills, as well as increased hyperactivity, impulsivity, and inattention in childhood and adolescence.

The study’s authors, Eliot Spindel, M.D., Ph.D., Elinor Sullivan, Ph.D., Owen McCarty, Ph.D., and Jason Hedges, M.D., Ph.D., hope that the findings will add to the limited existing literature on THC use during pregnancy and help guide patient counseling and cannabis-related public health policies in the future.

“It’s not common practice for providers to discuss cannabis use with patients who are pregnant or trying to conceive,” said the study’s corresponding author, Jamie Lo, M.D., M.C.R., associate professor of obstetrics and gynecology (maternal-fetal medicine), OHSU School of Medicine, and Division of Reproductive and Developmental Sciences at the ONPRC. “I hope our work can help open up a broader dialogue about the risks of cannabis use in the preconception and prenatal period, so we can improve children’s health in the long run.”

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