Prenatal marijuana use linked to serious risks for mother during pregnancy, study finds

Using marijuana during pregnancy carries risk for both mother and baby, studies say. (Halfpoint Images / Moment RF)

More and more people are using marijuana before or during pregnancy to ease nausea, pain, stress and help with sleep. In fact, research found that use has more than doubled in the last two decades.

Marijuana use in pregnancy has been linked to such adverse outcomes for the baby as lower birthweight, preterm birth and higher admission rates to neonatal intensive care units.

What about the potential danger to the mother if she uses cannabis before or during early pregnancy? According to a new study, the news there is alarming as well. There’s an increased risk of serious, potentially life-threatening maternal complications such as gestational hypertension and preeclampsia, which are both disorders of high blood pressure.

“Pregnant individuals who used versus did not use cannabis during early pregnancy had a 17 per cent greater risk of gestational hypertension (and) an 8 per cent greater risk of preeclampsia,” said lead study author Kelly Young-Wolff, a research scientist at Kaiser Permanente Division of Research in Pleasanton, California.

People who used marijuana in early pregnancy also had a “19 per cent greater risk of placental abruption,” Young-Wolff said.

In placental abruption, the organ that provides oxygen and nutrients to the fetus, called the placenta, suddenly detaches from the side of the uterus, thus endangering the health of the mother and the developing baby. A detached placenta is one of the leading causes of death in both expectant mothers and babies.

“Research suggests that pregnant people are bombarded with inaccurate messages from social media, cannabis retailers and peers suggesting that cannabis use during pregnancy is safe,” Young-Wolff said. “Our study provides timely and important data that adds to the growing body of evidence indicating that cannabis use during pregnancy is not safe.”

Compared to weight gain considered optimal for a successful pregnancy, people who used marijuana before or during early pregnancy were more 9 per cent more likely to gain too much weight and 5 per cent more likely to not gain enough weight during their pregnancies, the study found.

“To my knowledge, this is the largest study to date looking at cannabis use in pregnancy and adverse health outcomes in the mother,” said Brianna Moore, an assistant professor at the Colorado School of Public Health in Aurora, Colorado, in an email. Moore, who studies the use of cannabis in pregnancy, was not involved in the new research.

“It is never too late to cut back or limit your use of cannabis in pregnancy to minimize the potential health effects,” Moore said. “Talk to your healthcare provider.”

Serious, even life-threatening complications

Gestational hypertension is diagnosed when an expectant mother’s blood pressure rises above 140/90 after the first 20 weeks of pregnancy, typically receding back to normal after birth. Consistent high blood pressure during pregnancy can “hinder blood flow in many different organ systems in the expectant mother including the liver, kidneys, brain, uterus, and placenta,” according to the Children’s Hospital of Philadelphia.

For some women, gestational hypertension can develop into preeclampsia, a more serious form of high blood pressure in which increased blood levels of liver enzymes and protein in the urine are signs of possible kidney or liver damage in the mother. Blood platelet levels can decrease, and fluid can build up in the lungs, causing shortness of breath, according to the Mayo Clinic.

In extreme cases, such high blood pressure can lead to blood clots, seizures, stroke, temporary kidney failure and liver complications, according to the Cleveland Clinic.

“Preeclampsia can also lead to preterm delivery and admission in the neonatal intensive care unit, which separates the mom and baby at the time of birth and can interfere with that initial ability to bond skin-to-skin,” said OB/Gyn Dr. Deborah Ansley, medical director for the Kaiser Early Start prenatal health program in Northern California, in an email. She was not involved with the study.

How does marijuana cause such serious consequences during pregnancy? Experts believe that cannabinoids, including tetrahydrocannabinol, or THC, may bind to receptors in the placenta, disrupting estrogen signaling and affecting placental development and function.

THC is the part of the cannabis plant that creates euphoria, but more than 100 other cannabinoids have been identified in the cannabis plant, along with more than 500 other chemical substances.

Dangers highest with daily use

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 people were asked about their marijuana use when they entered into prenatal care at approximately 8 to 10 week’s gestation. Many of those patients also underwent urine analysis that could detect any marijuana use for the past 30 days.

More than 20,000 were identified as cannabis users — including nearly 11,000 expectant mothers who did not admit to marijuana use but tested positive by urinalysis.

“Our study was unique in that we had a large enough sample size to conduct a sensitivity analysis that limited the sample to pregnant patients who did not screen positive for any other substances,” Young-Wolff said.

“Importantly, results from 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 likelihood of developing gestational hypertension rose with the frequency of use, with daily users having the most risk.

“Our prior work has shown that the frequency of prenatal cannabis use is increasing 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 worrisome as the potency of marijuana today is much greater than in the recent past, experts say.

Using at least once a month or more was linked to a greater risk of placental abruption, the study found. In addition, there was an increased risk of eclampsia, a more serious form of preeclampsia that can lead to seizures and death, but the risk was not statistically significant, according to the study.

There was one unusual finding: a reduced risk for gestational diabetes. Studies in non-pregnant adults have been mixed about the impact of marijuana on insulin resistance and metabolic syndrome, a mix of health issues that can lead to diabetes and other chronic diseases, Moore said.

“More studies are needed to understand whether and how cannabis use in pregnancy may impact risk for gestational diabetes,” Moore said.

Discuss marijuana use with physicians

The study has limitations, the authors acknowledge. For one, they were not able to determine if marijuana use continued during the pregnancy.

“My suspicion is that the health effects would be stronger if the pregnant person continued to use cannabis after the first trimester, but more studies are needed,” Moore said.

Urine tests could only look for THC and no other cannabinoids, and the self-report could not determine if use was due to smoking or edibles, Young-Wolff said. In addition, since all of the expectant mothers were based in northern California, a state which legalized medicinal 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 be applicable to the general population since “the participants in this study were older, had higher incomes, and almost all had private health insurance,” Moore added.

As the known health risks for marijuana grow, pregnant women should feel free to discuss any cannabis use with their health care provider without fear of reprisal, experts say.

“If pregnant individuals are considering using cannabis during pregnancy to self-medicate pregnancy-related symptoms, we encourage them to discuss those symptoms with their doctor and use interventions recommended by clinical practice guidelines,” Young-Wolff said. “If pregnant individuals are not willing to quit using cannabis, we recommend that they try to use it less frequently.”