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More and more people are using marijuana before or during pregnancy to relieve nausea, pain, stress, and to help with sleep. In fact, research shows that use has more than doubled in the past two decades.
Marijuana use during pregnancy has been associated with negative outcomes for the baby, including lower birth weight, preterm birth, and increased neonatal intensive care unit admission.
What about the potential dangers to the mother if she uses cannabis before or during early pregnancy? According to a new study, the news is alarming there too. There is an increased risk of serious, potentially life-threatening complications for the mother, such as gestational hypertension and preeclampsia, both of which are conditions of high blood pressure.
“Pregnant individuals who used cannabis versus did not use cannabis during early pregnancy had a 17 percent greater risk of gestational hypertension (and) an 8 percent greater risk of preeclampsia,” said lead investigator Kelly Young-Wolff, a researcher at Kaiser Permanente Division of Research in Pleasanton, California.
People who used marijuana early in pregnancy also had a “19% greater risk of placental abruption,” Young-Wolff said.
In placental abruption, the organ that supplies oxygen and nutrients the fetus, called the placenta, suddenly detaches from the side of the uterus, endangering the health of the mother and the developing baby. A severed placenta is a leading cause of death in both expectant mothers and babies.
“Research suggests that pregnant women are bombarded with false messages from social media, cannabis sellers, and peers suggesting that cannabis use during pregnancy is safe,” Young-Wolff said. “Our study provides timely and important data that add to the growing evidence indicating that cannabis use during pregnancy is not safe.”
The study found that compared with the weight gain considered optimal for a successful pregnancy, people who used marijuana before or during early pregnancy were 9 percent more likely to gain too much weight and 5 percent more likely to gain too little weight during their pregnancy.
“To my knowledge, this is the largest study to date looking at cannabis use during pregnancy and adverse maternal health outcomes,” Brianna Moore, an assistant professor at the Colorado School of Public Health in Aurora, Colo., said in an email. Moore, who studies cannabis use during pregnancy, was not involved in the new research.
“It’s never too late to reduce or limit your cannabis use during pregnancy to minimize potential health effects,” Moore said. “Talk to your healthcare provider.”
Gestational hypertension is diagnosed when an expectant mother’s blood pressure rises above 140/90 after the first 20 weeks of pregnancy and typically returns to normal after birth. Persistently high blood pressure during pregnancy can “impair blood flow to many different organ systems of the expectant mother, including the liver, kidneys, brain, uterus and placenta,” according to the Children’s Hospital of Philadelphia.
In some women, gestational hypertension can develop into preeclampsia, a more serious form of high blood pressure in which elevated levels of liver enzymes and proteins in the urine are signs of possible kidney or liver damage in the mother. Platelet levels may drop and fluid can build up in the lungs, causing shortness of breath, the Mayo Clinic says.
According to the Cleveland Clinic, in extreme cases, such high blood pressure can lead to blood clots, seizures, strokes, temporary kidney failure and liver complications.
“Preeclampsia can also lead to preterm birth and admission to the neonatal intensive care unit, which separates the mother and baby at birth and can disrupt that initial opportunity for skin-to-skin attachment,” OB/Gyn Dr. Deborah Ansley, medical director of the Kaiser Early Start prenatal health program in Northern California, said in an email. She was not involved in the study.
How can marijuana have such serious effects during pregnancy? Experts believe that cannabinoids, including tetrahydrocannabinol, or THC, can bind to receptors in the placenta, disrupting estrogen signaling and affecting the development and function of the placenta.
THC is the part of the cannabis plant that causes euphoria, but over 100 other cannabinoids have been identified in the cannabis plant, along with over 500 other chemicals.
The study, published Monday in the journal JAMA Internal Medicine, used health data from Kaiser Permanente Northern California, which provides health care to 4.6 million people. More than 250,000 pregnant women were asked about their marijuana use when they came in for prenatal care at about 8 to 10 weeks of pregnancy. Many of those patients also underwent a urine test that could detect any marijuana use in the past 30 days.
More than 20,000 people were identified as cannabis users, including nearly 11,000 expectant mothers who did not admit to using marijuana but tested positive on urine tests.
“Our study was unique in that we had a large enough sample size to perform a sensitivity analysis that restricted the sample to pregnant patients who did not test positive for other substances,” Young-Wolff said.
“Importantly, the results of this analysis followed the same general pattern as the main findings, indicating that our findings were not attributable to the use of other substances during pregnancy,” she said.
The chance of developing gestational hypertension increased with frequency of use. Daily users were at greatest risk.
“Our previous work has shown that the frequency of prenatal cannabis use increases over time, with a greater proportion of those who use cannabis during pregnancy reporting daily use in recent years,” Young-Wolff said.
That’s especially concerning because the potency of marijuana is much greater today than in the recent past, experts say.
Using it at least once a month or more was associated with a higher risk of placental abruption, the study found. There was also an increased risk of eclampsia, a more severe form of preeclampsia that can lead to seizures and death, but the risk was not statistically significant, the study found.
There was one unusual finding: a reduced risk of gestational diabetes. Studies in nonpregnant adults have been mixed about marijuana’s impact on insulin resistance and metabolic syndrome, a mix of health problems that can lead to diabetes and other chronic diseases, Moore said.
“More research is needed to understand whether and how cannabis use during pregnancy may affect the risk of gestational diabetes,” Moore said.
The study has limitations, the authors acknowledge. First, they could not determine whether marijuana use continued during pregnancy.
“I suspect the health effects would be greater if the pregnant woman continues to use cannabis after the first trimester, but more research is needed,” Moore said.
Urine tests could only look for THC and not other cannabinoids, and self-report couldn’t determine whether use was due to smoking or edibles, Young-Wolff said. Additionally, since all of the expectant mothers were located in Northern California, a state that legalized medical cannabis in 1996 and adult-use sales in 2018, the results may not be generalizable to other populations in the United States.
The results may also not apply to the general population “because the participants in this study were older, had higher incomes, and almost all had private health insurance,” Moore added.
Experts say that the known health risks of marijuana are increasing, so pregnant women should feel free to discuss their cannabis use with their health care provider without fear of reprisal.
“If pregnant individuals are considering using cannabis during pregnancy to self-treat pregnancy-related symptoms, we encourage them to discuss these symptoms with their physician and use interventions recommended by clinical practice guidelines,” Young-Wolff said. “If pregnant individuals are not willing to stop using cannabis, we recommend trying it less often.”
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