Exposure to cannabis during pregnancy is associated with a 1.5 higher risk of unhealthy pregnancy outcomes, especially low birth weight.
Although the use of medical cannabis in the United States has more than doubled in the past decade, its full effects on health remain unknown, especially in vulnerable populations like pregnant people.
A new study from the University of Utah Health researchers included more than 9,000 pregnant people from eight medical centers across the U.S. Of those, 610 had detectable levels of cannabis exposure.
The researchers gauged cannabis exposure by measuring the levels of a metabolic byproduct of cannabis in the participants’ urine samples. The novel approach gave more accurate measurements than in previous studies, where participants reported their own cannabis use, underestimating the actual rate of use by two or three times.
Twenty-six percent of cannabis-exposed participants experienced an unhealthy pregnancy outcome, compared to 17% of non-exposed individuals.
The greater cannabis exposure was over the course of pregnancy, the higher the risks of unhealthy outcomes.
Cannabis use was most strongly associated with low birth weight but also increased the risk of pregnancy-related high blood pressure, stillbirth, and medically indicated preterm birth.
All of these conditions have been linked to reduced function of the placenta, which supplies the growing baby with oxygen and nutrients.
Low birth weight — less than 5 pounds or 2,500 grams — may have life-long consequences for a child’s health, such as delayed motor and social development and learning differences. Moreover, babies born at low weight are at a higher risk of developing heart disease, obesity, and diabetes later in life.
Cannabis is linked to long-term risks
The study does not explain how the use of cannabis leads to negative pregnancy outcomes. However, previous research in animal models suggested that long-term cannabis exposure can interfere with blood supply to the placenta.
"Cannabis use is not safe," says Robert Silver, M.D., professor of obstetrics and gynecology at U of U Health and the last author of the study. "It increases the risk of pregnancy complications. If possible, you shouldn’t use cannabis during pregnancy."
Torri Metz, M.D., vice chair of research of obstetrics and gynecology at the University of Utah Health and lead author on the study, explains that all modes of cannabis consumption, such as smoking and ingestion, ultimately need to be cleared from the body.
She told Healtnews, "Drugs are cleared from the body by moving into the bloodstream, and then they are processed by the liver and kidneys so that they can be metabolized and excreted. When cannabis metabolites are in the bloodstream, they cross the placenta to the fetus since the maternal and fetal circulation are connected."
The research authors urge patients who are considering using cannabis during pregnancy to have an open conversation with their doctor and choose safer remedies to alleviate nausea or anxiety.
The U.S. Food and Drug Administration strongly advises against using any cannabis products during pregnancy and while breastfeeding. This includes products containing cannabidiol (CBD), an active ingredient that does not produce high.
Currently, there is only one CBD product approved by the FDA called Epidiolex, which is aimed at treating seizures associated with epilepsy and other conditions.
Metz says the research looked specifically at metabolites of THC, a psychoactive constituent of cannabis.
"There is very little known about CBD specifically in pregnancy. Although, notably, many CBD products also contain THC. It will be important to continue to evaluate how different cannabis products affect pregnancy as there may be differential effects," she said.
Previous research has associated cannabis exposure during pregnancy with an increased risk of autism spectrum disorder and attention-deficit hyperactivity disorder in children.
Studies also suggest that children whose mothers used cannabis while pregnant were at a higher risk of developing depression, anxiety, and other mental health conditions.
As there is no known safe level of cannabis use during pregnancy, pregnant people should choose safer alternatives to alleviate pregnancy-related symptoms.