Cannabis in pregnancy linked to some maternal health problems

Large Kaiser Permanente study finds greater risk of pregnancy complications

Cannabis use during pregnancy is linked with health problems such as high blood pressure, preeclampsia, and weight issues, according to a large new Kaiser Permanente study published in JAMA Internal Medicine.

The findings were consistent with some previous studies of prenatal cannabis use but differed from others. The study authors said the findings are concerning and underscore the need for more research.

“These findings are worrisome, as they add to a growing body of evidence that cannabis is not safe to use during pregnancy,” said lead author Kelly Young-Wolff, PhD, MPH, a research scientist with the Kaiser Permanente Division of Research (DOR). “Previous research has focused on the health of the baby, and the relative lack of research on how prenatal cannabis use impacts maternal health is notable. Our study was designed to address this research gap with the goal of providing better data for clinicians to use when working with their patients to make more informed decisions about prenatal cannabis use.”

The researchers studied 316,722 pregnancies among more than 250,000 individual patients of Kaiser Permanente Northern California (KPNC) between 2011 and 2019. Cannabis use was measured by urine toxicology tests and a self-administered questionnaire, which are both given routinely at the entrance to prenatal care in KPNC.

The analysis found an increased risk of several health concerns among those who used cannabis during early pregnancy: gestational hypertension, or high blood pressure; preeclampsia, a serious complication of pregnancy; weight gain above or below guidelines for pregnancy; and placental abruption, the early separation of the placenta from the lining of the uterus during labor. For gestational hypertension, the researchers found the risk increased with more frequent reported cannabis use.

Patients using cannabis had a decreased risk of gestational diabetes. The authors said previous studies have been mixed on this question, and more research is needed to explore the impact of frequency of use and mode of administration – whether cannabis is smoked or taken in an edible form.

The study did not find increased risk of some other maternal health issues, such as eclampsia (a serious hypertensive condition that can cause seizures), placenta previa or placenta accreta (abnormalities in where the placenta grows in the uterus), or severe maternal morbidity.

The results were consistent with another large study that found people with cannabis use disorder had higher risk of gestational hypertension and preeclampsia. This suggests greater health risk with more frequent use, the authors said.

“The findings related to the frequency of use offer an important message for harm reduction,”  said study senior author Lyndsay Avalos, PhD, MPH, a DOR research scientist. “For patients who are not willing to stop using cannabis during pregnancy, decreasing use may pose lower risk of pregnancy complications.”

“Also, if our findings are replicated by other researchers, this could lead to interventions to reduce their risk of poor health outcomes,” Avalos added. “For example, patients who use cannabis in pregnancy might benefit from medical interventions to prevent preeclampsia, such as low-dose aspirin.”

More information helps women

The DOR study team has also examined prenatal cannabis use and infant health outcomes, and reported in the journal Obstetrics & Gynecology an increased likelihood of low birth weight and admission to the neonatal intensive care unit (NICU) for babies whose mothers used cannabis during pregnancy.

“Women may come across conflicting information about whether they can use cannabis safely during pregnancy, or if it is a good choice to manage pregnancy-related symptoms such as nausea,” said co-author Deborah Ansley, MD, regional medical director for KPNC’s Early Start prenatal health program. “Increasingly, research is suggesting the answer may be ‘no.’”

At the same time, Ansley said, patients need realistic and empathetic advice from their health care team, and to know they can discuss their substance use without stigma or fear of being reported to child protective officials. In California, prenatal cannabis use is not reportable to child welfare authorities.

The study was funded by the National Institute on Drug Abuse. It is part of an ongoing body of NIDA-funded work exploring prenatal cannabis use trends, adverse obstetrical and neonatal outcomes, maternal health outcomes, modes of cannabis administration, and effects of legalization in California.

Additional co-authors were Sara R. Adams, MPH, Stacey E. Alexeeff, PhD, Yeyi Zhu, PhD, Natalie E. Slama, MPH, and Monique B. Does, MPH, of the Division of Research; Lynn D. Silver, MD, MPH, of the Public Health Institute; and Carley Castellanos, LMFT, of Kaiser Permanente Northern California.

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About the Kaiser Permanente Division of Research

The Kaiser Permanente Division of Research conducts, publishes and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. It seeks to understand the determinants of illness and well-being, and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 600-plus staff is working on more than 450 epidemiological and health services research projects. For more information, visit divisionofresearch.kaiserpermanente.org or follow us @KPDOR.