A new guideline from the U.S. Food and Drug Administration advises pregnant women to stay away from marijuana as cannabis use during pregnancy is on the rise.

In 2009, researchers found about 4% of pregnant women tested positive for using cannabis during pregnancy, says Kelly Young-Wolff, a clinical psychologist for Kaiser Permanente. That number doubled to 8% in 2017.

Cannabis usage for younger age groups is increasing more rapidly — 22% of pregnant teenagers and 19% of pregnant young adults screened positive for using marijuana — a trend she calls “alarming.”

“I think pregnant women are inundated with messages from online media and from even cannabis dispensaries telling them that use in pregnancy is safe,” she says. “Unfortunately, that is not consistent with what we're seeing in our research studies.”

The FDA warns cannabis usage during pregnancy may affect fetal brain development because THC can enter the brain through the mother’s bloodstream. The guideline also warns breastfeeding while using cannabis can result in hyperactivity and poor cognitive function.

Young-Wolff says there's substantial evidence that shows using cannabis during pregnancy increases the risk of low birth weight, as well as problems with memory, problem-solving and concentration later in childhood.

Some moms’ groups are promoting cannabis use to alleviate symptoms like morning sickness, aches, nausea and other pregnancy symptoms, she says.

The growing social acceptability of cannabis thanks to legalization for recreational use in some states contributes to the spike in usage during pregnancy, too — and it’s also putting a lot of new products on the market.

The increasing number of ways to consume cannabis from vaping to edibles creates a challenge for researchers. Different studies have found conflicting results because of varying methodologies and failing to account for co-occurring substance use, she says.

Many studies on cannabis and pregnancy underestimate use because they are self-reported. Young-Wolff says women are twice as likely to screen positive for marijuana through urine toxicology testing than self-reporting.

Another challenge researchers face when studying pot and pregnancy is many studies looking at the health effects of using cannabis were conducted in the 1980s, but the potency of THC in marijuana has been increasing over time.

“It's unclear how that might impact the risks,” she says. “We don't really have a lot of new information yet to help us understand how these higher-potency products could impact the fetus.”

At Kaiser Permanente in northern California, Young-Wolff says the Early Start Screening and Intervention Program helps women quit substance use during pregnancy.

When a pregnant woman tests positive for cannabis use, the program connects them with a licensed social worker or a marriage and family therapist at the clinic with expertise in substance use during pregnancy.

Pregnant women can continue to meet the specialist throughout the pregnancy as needed, she says.

“I think it's important that women recognize that no amount of cannabis has been shown to be safe during pregnancy,” she says.

Cristina Kim produced this story and edited it for broadcast with Tinku Ray. Allison Hagan adapted it for the web.