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Marijuana use in pregnancy can diminish a child’s mental ability

Marijuana is legal in Washington and is often seen as “natural” or “safe.” As a result, some women don’t realize that using it during pregnancy may harm their baby. Or they may think it’s better to use marijuana to manage their morning sickness instead of a prescription. It’s not.

In my practice as a maternal fetal medicine doctor at Vancouver Clinic, I advise many pregnant mothers to stop using cannabis. Doctors and scientists are still discovering the full effects of marijuana in pregnancy. The data we do have suggests that it can have long-term impacts.

THC, the active compound in marijuana, crosses the placenta. This is important because substances that get through the placenta get to the baby. We also know that THC can accumulate in breast milk.

In animal studies, the offspring of females who were given marijuana had problems with learning and memory. They were also more likely to exhibit hyperactivity and exploratory behaviors. Human studies—specifically The Ottawa Prenatal Prospective Study and the Maternal Health Practices and Child Development Study—show similar results.

In these studies, elementary school-age children of regular marijuana users had difficulty:

  • Concentrating
  • Solving verbal reasoning problems
  • Solving visual memory problems.

Children of moms who used heavily in their first trimester had lower scores in reading, math, and spelling. When more complex thinking or behavior was required, kids who had been exposed to marijuana in utero were more likely to struggle.

It’s less clear how marijuana affects physical development and growth. We don’t know if marijuana poses a risk of birth defects or stillbirth. There’s also no clear link between birth weight and marijuana use. However one study in the Netherlands found that pregnancies exposed to marijuana use early on had a slight growth lag.

The American College of Obstetricians and Gynecologists recommends against using marijuana during pregnancy.

Women who are planning a pregnancy or who may become pregnant should avoid marijuana use, just as they should avoid alcohol and other drugs. Women who are already pregnant and are struggling with morning sickness should talk to their doctor. Self-medicating with marijuana is unsafe for the baby.

If you have questions about marijuana use or how to have a healthy pregnancy, talk to your doctor or midwife.