Aug. 29, 2024 – For nearly half a century, we’ve had a clear understanding of the risks of alcohol during pregnancy. Fetal alcohol syndrome emerged in the 1970s as a risk to children exposed to alcohol in the womb, and since then, many more women have abstained from its use. But the same is not true of marijuana, and, in fact, new research shows that a surprising number of women use it during pregnancy.
In an analysis of over 90,000 umbilical cord samples taken over the last 5 years, researchers at National Medical Services Labs, a laboratory testing services provider in Horsham, PA, found that nearly a fifth of those samples were positive for cannabis, another name for marijuana.
“More states are legalizing cannabis, so it’s more openly available and not as stigmatized as it once was,” said Kari Midthun, PhD, a forensic toxicologist at NMS Labs.
Marijuana use is increasing across all populations, and pregnant women are another group impacted by its newfound popularity. From 1992 to 2022, the rate of daily marijuana use in the U.S. increased by 15 times. What’s more, many think of cannabis as natural and safe during pregnancy. They may also turn to it to treat prenatal symptoms like morning sickness as well as anxiety and depression, said Alexandria Reinhart, an assistant laboratory director at NMS Labs.
The Maternal Risks of Marijuana
But even as its use expands, our understanding of its risks to pregnant women and their unborn babies is also increasing, said Kelly C. Young-Wolff, PhD, MPH, a clinical psychologist and research scientist at Kaiser Permanente.
Wolff’s research, focused on maternal health outcomes, found that those who used marijuana during early pregnancy had a 17% increased risk of pregnancy-induced high blood pressure, 8% higher risk of preeclampsia, and a 19% higher risk of placental abruption – a severe complication that happens when the placenta separates from the uterine wall before childbirth – compared to women who did not use the substance.
“A growing body of evidence indicates that cannabis use during pregnancy is not safe,” said Young-Wolff. She said patients should talk to their doctors about safer alternatives, depending on the prenatal or overlapping symptoms they’re having.
The Impact of Prenatal Marijuana Use on the Fetus
Marijuana use during pregnancy also presents risks to infants who are exposed to it in utero once it crosses the blood-brain barrier. The most common concern is low birth weight, said Torri Metz, MD, a maternal-fetal medicine expert at the University of Utah Health in Salt Lake City.
“People who use cannabis tend to have smaller babies, and it’s something that comes up again and again in the published literature,” she said.
Indeed, an analysis of 16 studies that included nearly 60,000 women, published in the journal JAMA Obstetrics and Gynecology, found an increased risk of preterm deliveries and decreased birth weight in newborns born to women who had used marijuana during pregnancy.
The long-term risks are trickier to know because a lot can happen once a child is born that may cause health issues down the line. But some research points to brain development problems as a result of marijuana use, said Kyle Walsh, PhD, an associate professor of neurosurgery and pathology at Duke University in Durham, NC.
“It’s associated with a higher risk of neurodevelopment conditions, most notably ADHD and also autism,” he said.
And perhaps even more concerning, Walsh said, is some of the research that his lab has been working on links marijuana use during pregnancy to some forms of childhood cancer. A study he authored, published in the journal Cancer Epidemiology, Biomarkers, and Prevention, found that prenatal use of marijuana was linked to a higher risk of central nervous system tumors, including a specific type of childhood brain tumor and a type of tumor of the eye.
The interesting part of the findings was that the cancers were related to precursors of neurons in the early brain, Walsh said. This means that unlike alcohol, which presents the most developmental risk in the second trimester, marijuana seems to do the most damage early in development, before many women might even realize they’re pregnant.
Walsh said that fetal neurodevelopment starts by 12-14 weeks of gestation, and many women could be using marijuana up until the point they find out they’re pregnant, which is often too late. “In some ways, by this time, the bus has already left the station,” he said.
Once women stop using marijuana, in some cases, the harm has already been done. For this reason, women need to consider marijuana use if they’re trying to get pregnant or if they think they could potentially get pregnant, especially considering that around 42% of pregnancies in the U.S. are unplanned.
Does the Mode of Use Matter?
In terms of how marijuana is used – for example, smoking vs. edible sources – research hasn’t yet determined if one vs. the other is more of a problem, Walsh said. But ultimately, the body has to process the marijuana no matter how its taken: It enters the bloodstream and crosses the placenta, potentially impacting the mother and unborn child along the way.
We don’t yet know whether products based on cannabidiol (CBD), a compound found in cannabis that does not contain THC, is also dangerous. But in the coming years, we’ll likely be looking into that as well, said Metz.
She said there’s a lack of education about cannabis use during pregnancy and that many of her patients aren’t aware of the risks that it can pose to their unborn child. Often, patients are using it for pregnancy-related symptoms, and doctors need to make their patients aware of safer alternatives.
For example, vitamin B6 supplements and over-the-counter medications such as doxylamine (Unisom) can be used for morning sickness that comes with with nausea as well as prenatal sleep issues. Also, depression and anxiety can be treated with a combination of therapy and certain prescription medications rather than marijuana.
The bottom line, Metz said, is that doctors need to make sure their patients understand the risks so they can stop marijuana use right away. While the research isn’t as concrete as it is for alcohol use during pregnancy, researchers say that in the coming years, it will be.
“For most, once they understand the risks, they stop using. That’s why having an open conversation with patients is so important,” Metz said.
