Marijuana use and pregnancy hardly go hand-in-hand for health reasons, but more American women are using marijuana just before and right after they become pregnant, new research warns.
"These findings should alert women's health clinicians to be aware of potential increases in daily and weekly cannabis use among their patients," said lead study author Kelly Young-Wolff. She is a research scientist at Kaiser Permanente, in Oakland, California.
In the study, the investigators analysed data on self-reported marijuana use among nearly 277 000 pregnant women (about 367 000 total pregnancies) in Northern California over nine years, from 2009 to 2017. California legalised recreational marijuana in 2018.
During that time period, the use of marijuana in the year before pregnancy rose from close to 7% to 12.5%, and the use of marijuana in early pregnancy (up to eight weeks' gestation) rose from nearly 2% to 3.4%, the findings showed.
Frequency of marijuana use also increased.
Among those who used marijuana in the year before pregnancy, daily users rose from 17% to 25%, weekly users increased from 20% to 22%, while monthly-or-less users fell from 63% to 53%, according to the report.
And among women who used marijuana early in pregnancy, daily users increased from 15% to 21%, weekly users rose from 25% to 27%, while monthly users decreased from 60% to 52%.
"The actual numbers are likely higher, as women may be unwilling to disclose their substance use to a medical professional," said Young-Wolff.
Still much that's unknown
There is significant evidence that marijuana exposure during pregnancy is associated with having a low-birthweight baby, the researchers said.
And women who are pregnant or planning to get pregnant should not use marijuana because it may impair foetal neurodevelopment, according to the American College of Obstetricians and Gynecologists.
"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 mode of cannabis administration and frequency of prenatal cannabis use," Young-Wolff said in a Kaiser news release.
The findings were published online in JAMA Network Open.
According to senior study author Dr Nancy Goler, "There is an urgent need to better understand the effects of prenatal cannabis exposure as cannabis becomes legalised in more states and more widely accepted and used." Goler is associate executive director of The Permanente Medical Group.
"Until such time as we fully understand the specific health risks cannabis poses for pregnant women and their foetuses, we are recommending stopping all cannabis use prior to conceiving, and certainly once a woman knows she is pregnant," she added.
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