Research found that babies born to mothers who used marijuana during pregnancy are much more likely to be born underweight.

The study, published by the Journal of the American Medical Association looked at data from more than 9,000 pregnant women across the United States.

Overall, the researchers found that the risk of low birth weight, medically induced preterm birth, stillbirth, and pregnancy-related high blood pressure in the moms-to-be “rose by nearly 30 percent in those who used cannabis while pregnant.”

Looking at the effects of prenatal marijuana use on infants’ health outcomes individually, the researchers found that marijuana use during pregnancy was associated with a 50 percent increase in the risk of low birth weight.

Birth weight is a concern because babies born underweight (less than 5 pounds, 8 ounces) have a higher risk of developing certain health problems and sometimes need special care in a neonatal intensive care unit after birth.

Past research has shown a possible link between prenatal marijuana use and negative health effects, but the study is important because more states have recently legalized marijuana for recreational use.

The study also supported prior research that found negative health outcomes in children whose moms used marijuana during pregnancy.

The study’s findings highlight the importance of screening pregnant women for marijuana use and advising them of the potential health effects.

Read more in the Journal of Pediatrics.