Pot Use in Pregnancy Linked to Low Birthweight

The fact that smoking pot in pregnancy is bad for baby is probably not a surprise. But there actually haven't been many scientific studies to prove it. Until now.

Pot Use in Pregnancy Linked to Low Birthweight Sadzak/Shutterstock

Not a shocker: Smoking pot in pregnancy is bad for baby. Although this seems like it would be obvious, there actually haven't been many scientific studies to prove it. But recent research published in the journal BMJ Open found a link between marijuana use in pregnancy and negative outcomes for baby, including low birth weight and more time in the NICU.

Pot's effects on baby

Researchers conducted a review of 24 studies that looked at cannabis (the internationally used term for marijuana) and pregnancy. Expectant moms who used pot were 36 percent more likely to have anemia (low iron), which can cause premature birth and low birth weight. In addition, "this review found that infants exposed to cannabis during pregnancy had a 77 percent higher likelihood of being underweight at birth, compared to infants whose mothers did not use cannabis," study author Cara Christ, M.D., M.S., director of the Arizona Department of Health Services, tells Fit Pregnancy. "Also, if the mother used cannabis during pregnancy, the likelihood of her infant needing to be placed in a neonatal intensive care unit was two times higher compared to those infants whose mothers did not use cannabis."

Although the study didn't explore exactly how weed affects the unborn baby, Dr. Christ has some ideas. "We know there is a potential for anything pregnant women eat or drink to cross the placenta and have an effect on their baby's health," she says. "This review found that use of cannabis during pregnancy may have some adverse effects on fetal health." The active chemical in marijuana, tetrahydrocannabinol (THC), may have negative effects on baby's brain development. Plus, pot smoke has the same harmful substances as tobacco smoke.

Related: Dangers of Smoking While Pregnant Mount

The need for better research

But, the problem with figuring out exactly how marijuana affects pregnancy is that it's usually used along with alcohol or cigarettes, which makes it hard to isolate the specific consequences of the pot itself. "As many cannabis users are often tobacco or alcohol users, determining a cannabis only effect is difficult," Dr. Christ says. Expectant moms who use pot also tend to be of a lower socio-economic level, which may mean that poorer prenatal care and nutrition could affect baby as well. Plus, because these studies relied on the women to self-report their marijuana intake, it's possible that they are not accurately reporting their amount of use. Even so, Dr. Christ holds her position that "there appears to be negative consequences for those that were exposed to cannabis."

Other drugs, like cocaine, have been well-researched. But the lack of research on marijuana use in pregnancy is becoming more concerning given the changing attitudes, and in some places legalization, of the drug. "I can't attest to popularity, but I can say the use of cannabis is gaining acceptability," Dr. Christ says. "As the acceptability of use increases, understanding the effects of cannabis exposure on maternal and fetal health becomes increasingly important." This is especially crucial as some pregnant women are now even smoking pot for morning sickness.

The disturbing results found in this review warrant a closer look at how marijuana affects pregnancy. "Less is known about the effects of cannabis on fetal growth and development, or its effects on pregnant women, [than other drugs]," Dr. Christ says. In the meantime, she says to think carefully about what you put in your body while pregnant. "We advise moms to try and take as few medications as possible during pregnancy, and avoid drugs and alcohol," she says. "We know proper prenatal care is one of the best ways to make sure babies are born healthy. This may include taking prenatal vitamins, making changes to your diet, and avoiding drugs or alcohol." If you use marijuana and are pregnant or planning to become pregnant, talk to your doctor about the risks. To get information on quitting, call 1-800-662-HELP or visit the Substance Abuse and Mental Health Services Administration at samhsa.gov.