Pregnant women who use marijuana daily may have delayed fetal growth

Marijuana use in pregnancy is on the rise, according to research.

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Marijuana use in pregnancy is on the rise, according to research.
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Hollis Johnson/Samantha Lee/INSIDER
  • An increasing number of women are using marijuana to cope with pregnancy symptoms like nausea, but there’s now evidence that using the substance daily could affect fetal development.
  • According to the study, pregnant women who used marijuana daily had fetuses with lower weights, smaller heads, and smaller abdomens in the third trimester compared to women who never used marijuana.
  • This isn’t the first study to suggest marijuana has adverse effects on pregnant women and their fetuses and babies.
  • Visit Insider’s homepage for more.

An increasing number of women are using marijuana to cope with pregnancy symptoms like nausea, but there’s now evidence that using the substance daily could affect fetal development.

According to the study, published in the December issue of The Journal of Maternal-Fetal and Neonatal Medicine, pregnant women who used marijuana daily had fetuses with lower weights, smaller heads, and smaller abdomens in the third trimester compared to women who never used marijuana.

Additionally, the third-trimester fetuses of daily users had reduced blood flow, which can affect physical growth. The researchers didn’t find significant differences between daily users and never-users in their first and second trimesters.

To come to their findings, researchers studied two groups of pregnant women between January 2013 and January 2017. The first group consisted of 442 women who had singleton pregnancies and reported daily marijuana use, and the second was a control group of 442 pregnant women with singleton pregnancies who never used marijuana. There were 55 women in their first trimester, 195 in their second, and 192 in their third for both groups.

The study didn’t follow these women through the birth of their babies, but according to the American Pregnancy Association, low fetal weights can cause babies to have low blood sugar, neurological disabilities, motor skill disabilities, lack of oxygen, or pneumonia when born.

Health experts have warned against marijuana use during pregnancy

Experts say there's real potential that marijuana use during pregnancy could be harmful.

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Experts say there’s real potential that marijuana use during pregnancy could be harmful.
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sruilk/Shutterstock

This isn’t the first study to suggest marijuana has adverse effects on pregnant women and their fetuses and babies.

One June 2018 study in Colorado, where recreational marijuana is legal, found that women who reported using it during their pregnancies had a 50% chance of lower birth weights. Because of evidence like this, the U.S. Surgeon General recently put out a warning regarding marijuana use during pregnancy.

Research has also shown using weed while pregnant can affect a child’s brain development. These studies found children of people who used marijuana during pregnancy had lower IQs, attention problems, and more impulsiveness compared to children whose mothers didn’t use marijuana while pregnant.

Still, “what we know today is pretty sparse,” Kjersti Aagard, a maternal-fetal medicine specialist and professor at Baylor College of Medicine and Texas Children’s Hospital, previously told Insider. “We don’t have the long-term studies to really examine that carefully from a public health perspective.”

There were also caveats to the present study, like the reliance on self-reported marijuana use. And because the study only found a link, but not a cause-and-effect relationship, between marijuana use and delayed fetal development, it’s possible factors unrelated to marijuana use affected the women’s fetuses.

The researchers of this new study hope their findings add to the small body of research on the substance and its pregnancy-related effects.

Until then, the researchers suggest women who use marijuana daily wean themselves off the substance in order to have the safest pregnancies possible and ask their doctors to screen them throughout pregnancy to monitor for potential fetal defects.