The number of women using cannabis in the year before they get pregnant and early in their pregnancies is increasing, and their frequency of use is also rising, claims a study.
The research, published in the journal of JAMA Network Open, examined self-reported cannabis use among 276,991 pregnant women and found that cannabis use has increased over time.
"These findings should alert women's health clinicians to be aware of potential increases in daily and weekly cannabis use among their patients. The actual numbers are likely higher, as women may be unwilling to disclose their substance use to a medical professional," said lead author Kelly Young-Wolff.
In addition, the prevalence of daily and weekly cannabis use may have risen even further in the past year and a half following legalisation of cannabis for recreational use.
Investigators were unable to differentiate whether self-reported cannabis use during pregnancy occurred before or after women were aware that they were pregnant.
Some women may use cannabis during pregnancy to manage morning sickness, the authors noted.
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The authors' previous work published in JAMA Internal Medicine found women with severe nausea and vomiting in pregnancy were nearly four times more likely to use cannabis during the first trimester of pregnancy.
Women may get the impression from cannabis product marketing and online media that cannabis use is safe during pregnancy, said Young-Wolff.
However, there is substantial evidence that exposure to cannabis in pregnancy is associated with having a low-birthweight baby, and obstetricians and gynecologists recommended women who are pregnant or contemplating pregnancy discontinue cannabis use because of concerns about impaired neurodevelopment and exposure to the adverse effects of smoking.
"There is still much that is unknown on the topic, including what type of cannabis products pregnant women are using and whether the health consequences differ based on the mode of cannabis administration and frequency of prenatal cannabis use," Young-Wolff noted.
"There is an urgent need to better understand the effects of prenatal cannabis exposure as cannabis becomes legalized in more states and more widely accepted and used," said study senior author Nancy Goler.
"Until such time as we fully understand the specific health risks cannabis poses for pregnant women and their fetuses, we are recommending stopping all cannabis use prior to conceiving and certainly once a woman knows she is pregnant," added Goler.