Lynn Singer of Case Western Reserve University School of Medicine in Cleveland said the researchers analyzed data on 96 pregnant women in England, as well as their babies at birth and at 4 months.
Singer said heavy ecstasy users were more likely to have babies who didn't meet development milestones for such things as coordination and balance. People who use ecstasy said it induces a sense of euphoria, a sense of intimacy with others and diminished anxiety, Singer said.
"The data so far suggests to us that there are effects of ecstasy that are harmful to the developing fetus," Singer said in a statement.
The study was published in the journal Neurotoxicology and Teratology.