MONDAY, April 7 (HealthDay News) -- Babies born to women who use cocaine, alcohol or tobacco during pregnancy may have brain structure changes that persist into early adolescence, a new U.S. study says.

Researchers at Children's Hospital Boston and the Boston Medical Center used MRI scans to study the brains of 35 children, average age 12, who were exposed to the substances while in the womb.

"We found that reductions in cortical gray matter and total brain volumes were associated with prenatal exposure to cocaine, alcohol or cigarettes," study first author Dr. Michael Rivkin, a neurologist at Children's Hospital Boston, said in a prepared statement.

The more substances a child was exposed to, the greater the reduction in brain volume.

The study, published in the April issue of the journal Pediatrics, is the first to document joint long-term effects of prenatal cocaine, alcohol and tobacco exposure on brain structure, Rivkin said.

Previous studies that documented brain effects of prenatal alcohol exposure were mostly limited to children with fetal alcohol syndrome. Children with that condition were excluded from this new study.

Rivkin noted that his study was too small to find statistically significant effects of single substances after factoring in exposure to other substances, and was also too small to document the effects of different levels of prenatal exposure.

However, Rivkin said the overall findings are highly suggestive, and he and his colleagues would like to continue their research into this important public health matter. It's estimated that more than one million babies born each year in the United States have been exposed to at least one of these substance while in the womb.

Health-care providers should offer pregnant women comprehensive care to help them reduce the use of all harmful substances. And public health campaigns shouldn't ignore the risks of some substances while focusing on others, since the greater the number of total prenatal exposures, the more likely there will be harmful and lasting effects on a baby's developing brain, the study authors said.

More information

The American Pregnancy Association has more about pregnancy wellness.