Pregnant Women Turn to Marijuana, Perhaps Harming Infants

During her pregnancy, she never drank alcohol or had a cigarette. But nearly every day, Stacey, then 24, smoked marijuana.

With her fiancé’s blessing, she began taking a few puffs in her first trimester to quell morning sickness before going to work at a sandwich shop. When sciatica made it unbearable to stand during her 12-hour shifts, she discreetly vaped marijuana oil on her lunch break.

“I wouldn’t necessarily say, ‘Go smoke a pound of pot when you’re pregnant,’” said Stacey, now a stay-at-home mother in Deltona, Fla., who asked that her full name be withheld because street-bought marijuana is illegal in Florida. “In moderation, it’s O.K.”

Many pregnant women, particularly younger ones, seem to agree, a recent federal survey shows. As states legalize marijuana or its medical use, expectant mothers are taking it up in increasing numbers — another example of the many ways in which acceptance of marijuana has outstripped scientific understanding of its effects on human health.

Often pregnant women presume that cannabis has no consequences for developing infants. But preliminary research suggests otherwise: Marijuana’s main psychoactive ingredient — tetrahydrocannabinol, or THC — can cross the placenta to reach the fetus, experts say, potentially harming brain development, cognition and birth weight. THC can also be present in breast milk.

“There is an increased perception of the safety of cannabis use, even in pregnancy, without data to say it’s actually safe,” said Dr. Torri Metz, an obstetrician at Denver Health Medical Center who specializes in high-risk pregnancies. Ten percent of her patients acknowledge recent marijuana use.

In the federal survey, published online in December, almost 4 percent of mothers-to-be said they had used marijuana in the past month in 2014, compared with 2.4 percent in 2002. (By comparison, roughly 9 percent of pregnant women ages 18 to 44 acknowledge using alcohol in the previous month.)

Young mothers-to-be were particularly likely to turn to marijuana: Roughly 7.5 percent of 18- to 25-year-olds said they had used pot in the past month in 2014, compared with 2 percent of women ages 26 to 44.

Evidence on the effects of prenatal marijuana use is still limited and sometimes contradictory. Some of the most extensive data come from two sets of researchers, in Pittsburgh and in Ottawa, who have long studied children exposed to THC in the womb.

In Pittsburgh, 6-year-olds born to mothers who had smoked one joint or more daily in the first trimester showed a decreased ability to understand concepts in listening and reading. At age 10, children exposed to THC in utero were more impulsive than other children and less able to focus their attention.

Most troubling, children of mothers who used marijuana heavily in the first trimester had lower scores in reading, math and spelling at age 14 than their peers.

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