A Kaiser Permanente study, published today in JAMA Internal Medicine, found that women with mild and severe nausea and vomiting in pregnancy were significantly more likely to have used marijuana during pregnancy than women without these symptoms.
Recent studies have shown that the prevalence of marijuana use among pregnant women is increasing, but little is known about what has contributed to these increases. One hypothesis is that pregnant women use marijuana to treat symptoms of morning sickness, but few studies have examined the association between nausea and vomiting in pregnancy and prenatal marijuana use.
The new study of more than 220,000 pregnancies in Northern California found that pregnant women with severe nausea and vomiting in pregnancy had nearly four times greater odds of prenatal marijuana use than pregnant women without nausea and vomiting. Those with mild nausea and vomiting had more than two times greater odds of prenatal marijuana use.
“This is the largest study to date of nausea and vomiting in pregnancy and prenatal marijuana use,” said the study’s lead author, Kelly Young-Wolff, Ph.D., MPH, a research scientist at Kaiser Permanente’s Division of Research in Northern California. “Our findings add important evidence to a small but growing body of research suggesting that some pregnant women may use marijuana to self-medicate morning sickness.”
The women in the study were Kaiser Permanente members in Northern California who completed a self-reported substance use questionnaire and urine toxicology test in the first trimester. Nausea and vomiting in pregnancy in these members was identified based on diagnostic medical codes in the electronic health record during the first trimester.
The prevalence of prenatal marijuana use among the 220,510 women who received the screening in the first trimester was 5.3 percent, which is consistent with national statistics.
Severe nausea and vomiting in pregnancy occurred in 2.3 percent of the pregnant women, and 11.3 percent of them used marijuana during pregnancy. Mild nausea and vomiting in pregnancy occurred in 15.3 percent of the group, and 8.4 percent of them used marijuana during pregnancy. Marijuana use by women with no nausea and vomiting in pregnancy was 4.5 percent.
The results are consistent with the hypothesis that women use marijuana to self-medicate for nausea and vomiting in pregnancy, but the study cannot rule out other possible explanations, such as whether marijuana use contributes to nausea and vomiting in pregnancy, or whether clinicians diagnose nausea and vomiting in pregnancy more frequently among women who report using marijuana to treat it.
The study used Kaiser Permanente members in Northern California who were screened for marijuana use in the first trimester of pregnancy and the results may not generalize nationally, or to women without health care, or those who enter prenatal care late.
National guidelines recommend pregnant women discontinue marijuana use due to concerns about the potential for impaired fetal neurodevelopment, low birth weight and exposure to the adverse effects of marijuana smoke, but additional research on the health effects of prenatal marijuana exposure are needed. The guidelines recommend patients with nausea and vomiting in pregnancy should be screened for marijuana use and educated about effective and safe treatments for nausea and vomiting in pregnancy.
“We hope our study can help alert clinicians to the fact that women with nausea and vomiting in pregnancy are more likely to use marijuana,” said the study’s senior author, Nancy Goler, MD, a Kaiser Permanente OB-GYN in Northern California and associate executive director for The Permanente Medical Group. “Pregnant women need to be screened and given the information about the possible negative effects, while also receiving medically recommended treatment options.”
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