Carried out by researchers at Kaiser Permanente, the large-scale study looked at 220,510 pregnant women who were Kaiser Permanente members in Northern California.
The women were asked to self-report on any substance use through a questionnaire and complete a urine toxicology test in the first trimester, with the researchers assessing any nausea and vomiting using electronic health records.
They 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, and 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. "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."
However, the researchers added that the study cannot rule out other possible explanations, such as whether using marijuana contributes to nausea and vomiting in pregnancy, or whether nausea and vomiting is diagnosed in pregnancy more frequently among women who report using marijuana to treat it.
National guidelines recommend that women stop marijuana use during pregnancy due to concerns that the drug may impair fetal neurodevelopment and contribute to low birth weight.
"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. "Pregnant women need to be screened and given the information about the possible negative effects, while also receiving medically recommended treatment options."
The results can be found published online in the journal JAMA Internal Medicine.