Study links marijuana use in pregnant women to health risks

A study has found that pregnant women who use marijuana are more likely than those who do not to experience health complications that earlier research has linked to preterm birth.

Research published Monday in JAMA Internal Medicine found that pregnant women using cannabis were 17% more likely to develop pregnancy-induced hypertension, 19% more likely to experience the painful separation of the placenta from the uterus and 8% more likely to get preeclampsia. The latter condition is marked by high blood pressure and protein spikes in urine, indicating damage to the kidneys or other organs.

The study also found pregnant women using cannabis had a 5% greater risk of gaining too little weight and a 9% risk of putting on too many pounds than is healthy for childbearing.

Three researchers from Kaiser Permanente analyzed the electronic health records of 316,722 early-stage pregnancies the health system recorded in Northern California from 2011 to 2019.

Their investigation is the first to control for issues that led previous researchers to underestimate cannabis use based on self-reporting, said Kelly Young-Wolff, the lead author of the study.

She said her team screened out the presence of other substances and included the results of a drug urine test for THC, the psychoactive substance in cannabis.

“With legalization, there has been an increase in alternative forms of cannabis administration, including vaping and edibles,” said Ms. Young-Wolff, a clinical psychologist and research scientist at the Kaiser Permanente Northern California Division of Research. “The relative risks associated with different routes of cannabis administration during pregnancy are unknown and warrant additional research.”

The study comes as a growing number of states have legalized recreational marijuana, putting pressure on public officials to lift federal prohibitions.

Public surveys have shown cannabis use surging in recent years, surpassing cigarettes among young people.

The findings published Monday add to a growing body of research linking marijuana use during pregnancy to increased risks of preterm birth, lower birth weight, undersized babies and admission to neonatal intensive care.

Reached for comment, some medical experts not involved in the study said it highlights an urgent need to regulate and restrict marijuana like other addictive substances.

“The bottom line is that cannabis use during pregnancy should be discouraged just as alcohol and cigarette use is,” said Dr. Dimitri Christakis, a pediatrician, an investigator and professor at the Seattle Children’s Research Institute, affiliated with Seattle Children’s Hospital and the public University of Washington.

Dr. Ruth Milanaik, a developmental-behavioral pediatrician at the Steven and Alexandra Cohen Children’s Medical Center of New York, said the time has come to make cannabis dispensaries slap pregnancy warning labels on THC-based products.

“Cannabis providers must warn of the dangers to both fetus and mother, and doctors should counsel against cannabis use during pregnancy,” said Dr. Milanaik, who researches the issue.

Ob Hospitalist Group, which supplies OB/GYN doctors to hospitals nationwide, said the study only addressed some of the health problems that have surfaced as marijuana use grows among pregnant women.

“This large study didn’t show issues surrounding abnormal fetal growth and fetal growth restriction, which has been shown in other studies to lead to neonatal complications,” said Dr. Eric Colton, an Illinois-based OB/GYN who belongs to the group. “It highlights the fact that the more we encounter marijuana use during pregnancy, we are uncovering more complications.”