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Cannabis use in pregnancy may raise infant health risks

Large Kaiser Permanente study adds to evidence about low birthweight, preterm birth, admission to neonatal intensive care

A large study of more than 360,000 mothers and infants found increased likelihood of low birth weight and admission to the neonatal intensive care unit (NICU) for babies whose mothers used cannabis during pregnancy. The Kaiser Permanente analysis was published in the American Journal of Obstetrics & Gynecology.

Lyndsay Avalos, PhD, MPH

The findings align with previous research suggesting a connection between prenatal cannabis use and low birthweight babies, and advice from the American College of Obstetricians and Gynecologists that pregnant patients avoid cannabis in pregnancy.

“This is a large, well-designed study that adds important evidence about potential poor outcomes for babies when cannabis is used in pregnancy,” said lead author Lyndsay Avalos, PhD, MPH, a research scientist with the Kaiser Permanente Division of Research. “Our analysis adds new concerns about the potential for preterm birth and NICU admission, which are associated with immediate, highly stressful situations for the family as well as long-term adverse outcomes for the child.”

The researchers also found a “dose-response” relationship, meaning increasing risk of infant health risks with more frequent reported use of cannabis.

The analysis used health records from 364,924 infants born to Kaiser Permanente Northern California (KPNC) members between January 2011 and July 2020. Of these, 6.2% of the infants were exposed to cannabis in utero. Information about cannabis use was obtained from a self-report prenatal screening questionnaire and a urine toxiciology test.

The study found statistically significantly greater odds of low birthweight, baby that is small for gestational age, preterm birth, and admission to a NICU.

Kelly Young-Wolff, PhD, MPH

The analysis adjusted for other variables, such as maternal socioeconomic status, other substance use, medical and mental health conditions such as obesity, and adequacy of prenatal care, to rule out those factors as influencing the findings.

Pregnant patients can use this information to make more informed choices about cannabis use in pregnancy, said senior author Kelly Young-Wolff, PhD, MPH, a DOR research scientist. “Pregnant individuals want information about what health risks they should be concerned about,” Young-Wolff said. “This study involves a large number of patients, and replicates what previous research has shown.”

“Also, the finding of greater risk with more frequent use provides an important harm reduction message,” Young-Wolff added. “For those who may not be willing to stop using cannabis during pregnancy, less frequent use may have fewer potential harms.”

The study team has published widely on trends in prenatal cannabis use. Their work has shown increasing use among KPNC members, and associations with patients who also have nausea, depression, anxiety, and trauma, suggesting they may be using cannabis to control their symptoms. The researchers have also published insights from focus groups of people who have used cannabis during pregnancy, who said they welcome non-judgmental dialogue with their obstetrical medical team about managing prenatal symptoms and cannabis use.

Deborah Ansley, MD

Clinicians can use these findings to bolster their message to patients about weighing risks of substance use in pregnancy, said study co-author Deborah Ansley, MD, regional medical director for KPNC’s Early Start prenatal health program. “The clinician can be most effective by learning the patient’s symptoms and reasons they may be using cannabis, and following that with a factual and non-judgmental conversation about risks of cannabis and other treatment options in pregnancy.”

The study was funded by the National Institute on Drug Abuse.

Additional co-authors were Sara R. Adams, MPH, Stacey E. Alexeeff, PhD, Nina Oberman, MPH, and Monique B. Does, MPH, of the Division of Research; Nancy Goler, MD, of Kaiser Permanente Northern California; and Alisa A. Padon, PhD, and Lynn D. Silver, MD, MPH, of the Public Health Institute.

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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 or follow us @KPDOR.


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