- Researchers say they looked at 9,000 pregnancies and concluded cannabis is associated with a number of unhealthy pregnancy outcomes.
- They noted that they used testing rather than self-reporting, as in other studies, because of the amount of contradictory information about cannabis’ effect on pregnancies.
- The researchers concluded that exposure to cannabis was associated with a 1.5-fold increase in risk for people who are pregnant.
Despite cannabis being used as a remedy for a variety of health issues the past decade as legalization becomes more prevalent, its effect on pregnant women has been uncertain.
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The University of Utah researchers looked at more than 9,000 pregnant women from eight medical centers across the United States.
They concluded that cannabis is associated with “a composite measure of unhealthy pregnancy outcomes, especially low birth weight, and that higher exposure is associated with higher risks.”
The study authors wrote that in the past decade the percentage of people in the United States using medical marijuana has more than doubled due to legalization in many states.
They also wrote that their study was larger and measured cannabis exposure more accurately, which had the effect of better distinguishing cannabis’ effects from those caused by other correlated health conditions.
“Cannabis use is not safe,” said Dr. Robert Silver, a University of Utah professor of obstetrics and gynecology and one of the study’s authors, in a statement. “It increases the risk of pregnancy complications. If possible, you shouldn’t use cannabis during pregnancy.”
The study authors added that they wanted to answer questions about the safety of cannabis during pregnancy, at least partially because of contradictory information many people get trying to learn about the health effects of cannabis.
“There’s so much information out there — discussion and social media channels and on the internet — about cannabis use and pregnancy,” said Dr. Torri Metz, the vice chair of research of obstetrics and gynecology at University of Utah and the study’s lead author, in the statement. “I think it’s hard for patients to understand what they should be worried about, if anything.”
The research team said some studies found no association between cannabis use and pregnancy complications. Metz said part of the reason why different studies get differing results on cannabis and pregnancy is there are “so many differences between baseline characteristics of people who use and don’t use cannabis during pregnancy. There’s different rates of anxiety and depression.”
The recent study measured the levels of a metabolic byproduct of cannabis in urine samples, which researchers said gave more accurate measurements of exposure than in previous studies that relied on subjects’ self-reporting their use. The latter underestimated the actual cannabis use rate by two or three times, they said.
The differences can affect risks during pregnancy, making it difficult to assess the consequences related specifically to cannabis.
Researchers said the large study size also helped.
Among the subjects, 610 showed detectable levels of cannabis exposure, meaning the team could statistically untangle cannabis impact from other factors such as nicotine exposure, pre-existing health conditions, and socioeconomic status.
The researchers said exposure to cannabis was associated with a 1.5-fold increase in risk. They added that 26% of pregnant people exposed to cannabis had an unhealthy pregnancy outcome compared to 17% of pregnant people who weren’t exposed. Higher risks over the course of pregnancies came with higher exposure levels.
Researchers examined an aggregate measure of negative health outcomes, such as stillbirth, pregnancy-related high blood pressure, low birth weight, and medically indicated preterm birth.
They said these conditions have been linked to reduced function of the
The study authors said their research couldn’t determine why cannabis is linked with negative pregnancy outcomes, but
The study data was collected from 2010 to 2014, when products were just hitting the market and the THC (the psychoactive ingredient in cannabis) content in newer products has increased. Silver said the greater risk they found in higher levels of exposure was especially concerning. The effects of the newer products remain mostly unknown.
The team urged pregnant women considering using cannabis to talk with their doctor. Pregnant people often use cannabis for nausea or anxiety, but other remedies have been proven to be safe.
“There are many, many reasons people use cannabis,” Silver said. “But there may be alternative therapies that can help mitigate the symptoms.”
Dr. G. Thomas Ruiz, the lead OB/GYN at MemorialCare Orange Coast Medical Center in California, told Medical News Today he’s not sure doctors specifically knew cannabis was associated with low birthweight babies by compromising placenta function. However, it didn’t stop them from trying to dissuade pregnant women from using cannabis.
“We were very aware of the limited data available of the results of cannabis use during pregnancy and in general have advised cannabis users against using cannabis in pregnancy, like the recommendations we make with other products, such as alcohol or tobacco,” said Ruiz, who was not involved in the study. “There are also many medications which are safe to use outside of pregnancy, but that we advise their discontinuation during pregnancy because of its effect on the developing fetus.”
Ruiz said how the cannabis is ingested probably isn’t important.
“What is important is the blood level of THC within the mother and the amount of THC, which crosses the placenta into the developing fetus,” Ruiz said.
Dr. Adi Davidov, the associate chair and director of obstetrics and gynecology at Staten Island University Hospital in New York, told Medical News Today most doctors just assume cannabis is unsafe during pregnancy.
“There have been many observational studies looking at this question that have shown higher pregnancy complication rates,” said Davidov, who was not involved in the study. “Unfortunately, in an observational trial, it is hard to prove that there is a direct link, as there are usually confounding factors. It is unlikely that we will ever have a truly randomized controlled trial regarding this issue.”
“There is enough observational data in the medical literature that shows that exposure to marijuana possibly increases poor obstetric as well as neonatal outcome,” he added.
Dr. Greg Marchand is an OB-GYN in Arizona who was not involved in the study. He told Medical News Today this is the first study he’s aware of that disregards subjects’ self-reporting and goes only by lab testing, a method he says “has a lot of value.”
“That’s going to take out a lot of moms who occasionally use and might have evaded testing otherwise,” Marchand said. “It’s also a rather large study, so it adds a lot to the evidence.”
Marchand said how the cannabis is ingested could make a difference.,
“It is entirely possible that all of the ill effects seen in this study and many others exist only because of the inhalation of the smoke, not the actual marijuana,” he said. “This logically makes sense as similar ill effects are seen when pregnant woman smoke cigarettes. It is very difficult to subgroup out people who only exclusively inhale vapors or ingest edibles, as this is a small minority of marijuana users.”
Marchand said he always tells patients not to smoke marijuana during pregnancy, but it could be a different story if they’re using edibles or vaping for anxiety, chronic pain, or other medical conditions.
“Regardless of method of ingestion, if they are only using it recreationally – i.e. to get high – I recommend discontinuing for the course of pregnancy,” he said.