The debate is on about smoking during pregnancy. But what about smoking dagga?
An analysis of urine samples from roughly 300 000 California women finds that more than 7% used marijuana while pregnant.
What's more, rates of pot use in pregnancy have steadily risen over the years – from 4.2% of women in 2009 to 7.1% just seven years later.
That's according to the new report from Kaiser Permanente Northern California, a major regional health care group.
The study was published in JAMA.
What did the report entail?
"Use among [pregnant] females younger than 18 to age 24 years increased the most," added the team led by Kelly Young-Wolff, a Kaiser researcher in Oakland.
Among this youngest group, use of pot during pregnancy rose from 12.5% in 2009 to nearly 22% by 2016.
Rates of use were highest among the young, and dropped steadily as age rose during pregnancy, the researchers said.
Not necessarily deliberate use
There was one important caveat to the survey: Urine samples were taken at eight weeks of gestation, so pot use might have occurred before many of the women realised they were pregnant. Pot can linger in the system for up to 30 days, the researchers noted.
But the researchers believe that urine samples are likely to provide the most accurate picture of marijuana use in pregnancy, because people tend to hesitate about admitting such behaviours.
Prior US studies had suggested that marijuana use was on the rise in pregnancy, "however, [those] studies are limited to self-reported surveys," Young-Wolff's group noted.
Even in the Kaiser study, women's self-report of marijuana use in pregnancy was considerably lower than that revealed by urine samples.
Impaired foetal growth
Why the trend? The growing acceptance of marijuana may be a driving factor, the researchers said.
"In California, medical marijuana was legalised in 1996, and prenatal use may further escalate in 2018 when recreational marijuana is available legally," the Kaiser team noted.
Whatever the reasons, the findings could be bad news for babies, since "initial evidence suggests that prenatal marijuana may impair foetal growth and neurodevelopment," Young-Wolff's group said.
Many women may not understand the potential risk, however. According to one survey conducted between 2007 and 2012, 79% of women "reported perceiving little to no harm in prenatal [pot] use," the Kaiser team noted.
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