Just how bad is cocaine use during pregnancy?

People know that cocaine use during pregnancy is bad, but a new study shows that it's linked to having smaller, more premature babies.

"This actually gives us concrete numbers to remind us once again of the association of cocaine use and (the) negative impact that it has not only on pregnancy but also on newborn babies," said Dr. Kellie Murphy, co-author of the study in the American Journal of Obstetrics and Gynecology.

Women who used cocaine while pregnant had about a one in three chance of having an underweight baby, while women who did not had about a one in 10 chance. An underweight baby is defined as weighing less than 2,500 grams, or about five and a half pounds.

When Murphy and her colleagues looked at data from a number of previous studies, they found that babies born to cocaine-using mothers also had a one in three chance of being born before 37 weeks of pregnancy. They defined cocaine use during pregnancy as any use at all.

Without cocaine use, this risk was about one in eight. A normal term birth is between 37 and 41 weeks, according to Children's Hospital in Boston.

This means they're "small in weight, size and head circumference, the brain's smaller, everything is smaller," Murphy, an associate professor of obstetrics and gynecology at the University of Toronto, told Reuters Health.

These babies typically have a harder time eating, and are more likely to be sick in their first year. Other research has shown that being born too small or too early can lead to long-term health problems, such as developmental delays and lower IQs when these babies get older, she said.

They may also have a higher risk of high blood pressure, heart disease and early death, said Dr. Dotun Ogunyemi, the vice chair of education in obstetrics and gynecology at Cedars-Sinai Medical Center in Los Angeles, who was not involved in the study.

"Thus if we want the next generation to be fit, healthy and adjusted, health care policy needs to address" the health of these babies, he told Reuters Health by email.

The researchers grouped together 31 previous studies and looked at exactly how cocaine affected babies in a large number of births. None of the previous studies was very large. By combining studies, the researchers could get a better idea of how much of an effect cocaine use has on babies, Murphy said.

This is validating what health care workers already knew, Ogunyemi said. But it does raise the larger social problem of how to help pregnant women addicted to drugs.

"Many of the women addicted to cocaine are disadvantaged on many levels," he said. "Many of these women cannot break the cycle of addiction."

The study took these other factors into account, but women who use cocaine while they're pregnant also tend to use other drugs, smoke, be poor, and often don't get good prenatal care, the researchers said.