By Linda Carroll
(Reuters Health) - Increasing numbers of pregnant women are using marijuana in the U.S. and that may result in issues for their babies, two new studies suggest.
Researchers found that the proportion of U.S. women using pot during pregnancy more than doubled between 2002 and 2017, according to a report published in JAMA.
Legalization may at least partly explain why more women are using marijuana since many assume that means the drug is safe, said the U.S. study's lead author, Dr. Nora Volkow, director of the National Institute on Drug Abuse. That attitude, coupled with the lack of studies on pot can lead to "magical thinking," Volkow said. "It's very appealing to think that a drug that makes us feel great could come with no ill effects."
But in the case of pregnant women, "you're talking about the health not just of the mother, but of a second person who could potentially be harmed," Volkow said, adding she was especially surprised to find the proportion of pregnant women using pot daily had more than tripled.
Volkow's study analyzed data on 467,100 women aged 12 through 44 who participated in the National Survey on Drug Use and Health.
Between 2002 and 2017, cannabis use rose from 3.4% to 7.0% of pregnant women overall and daily use increased from 0.9% to 3.4% of pregnant women. Use during the first trimester increased from 1.8% to 5.3% and from 0.6% to 2.5% during the second trimester. In 2013-2017, just 0.5% of pregnant women asked if they were using cannabis at the recommendation of a clinician said they were.
A Canadian study in the same journal found that when pregnant women used cannabis, their babies were more likely to be born early, at a lower weight and to be transferred to a neonatal intensive care unit. Also, the placenta was more likely to detach from the uterine wall, potentially depriving the baby of oxygen, when mothers used cannabis. Newborns of cannabis users also had a higher risk of low scores on a test that evaluates neonatal status.
"These risks are concerning because, for example, being born small is related to other complications in newborns and higher rates of certain diseases later in life," said the Canadian study's lead author, Daniel Corsi, an epidemiologist and adjunct professor at the University of Ottawa.
Overall, the study involved 5,639 pregnant pot users and 9,427 nonusers enrolled in Ontario's Better Outcomes Registry & Network.
Corsi suspects many of the women using pot were battling pregnancy-related nausea, since there was a decline in use after the first trimester.
"Many women, from social media, are finding that cannabis is good for morning sickness," Corsi said in an email. "We want to emphasize a critical message for providers to speak with pregnant women about cannabis use and communicate that it is not a low-risk activity."
It's possible the numbers of women using pot during pregnancy may not actually be increasing, but rather that more women are feeling comfortable admitting they are using marijuana now that it's legal and more socially acceptable in Canada, said Dr. Kristina Mark of the University of Maryland School of Medicine in Baltimore.
If that's true, it's good news because women may be more likely to discuss the issue with their doctors, said Mark, who was not involved in the new research. "If it's an actual increase, that is problematic," she said. And that's because no one really knows the full impact of cannabis on fetuses because there have been so few studies on the drug due to government regulations.
While both new studies have some weaknesses, in particular their dependence on self-reported marijuana use, they help shed light on the issue, Mark said.
The lack of science on the subject is sometimes construed as meaning that pot is safe, Mark noted, but "absence of evidence is not evidence of absence."
There are some undeniable facts. First is that the active ingredient in marijuana, THC, crosses the placenta, so every time a mom smokes a joint, the baby is doing so, too, Mark said. "For some people that doesn't seem dramatic," she added. "They say, 'I get high and then I continue on with my life.' But these babies are being exposed during a time of rapid development, particularly neurodevelopment."
SOURCE: https://bit.ly/2WWm0C9 , https://bit.ly/2L5Hple and https://bit.ly/2RqjM83 JAMA, online June 18, 2019.