By Anne Harding
Among 35 children 10 to 14 years old, those whose mothers had used cocaine, drank alcohol, or smoked tobacco or marijuana while they were pregnant tended to have a smaller head circumference than their peers who weren't exposed to these substances prenatally.
The differences seen with use of a single substance were not statistically significant, but became so when a child was exposed to two or more of them.
While the findings suggest no single substance has a "devastating" effect on the foetal brain, Dr. Michael J. Rivkin of Children's Hospital and Harvard Medical School in Boston, the study's lead author, told Reuters Health, they do show that a combination of them quite possibly will. "There is no smoking gun," he said in an interview.
Rivkin and his team used an imaging technique called magnetic resonance imaging to measure the volume of different types of brain tissue in the study participants, and also measured head circumference.
Exposure to each single substance was tied to a smaller head circumference, lower volume of grey matter (the portion of the brain containing nerve cell bodies), and lower total brain volume.
While the single exposures did not have a statistically significant effect, exposure to a combination of two substances did produce significant reductions in the three measures of brain size.
And the difference grew with the number of exposures, with children exposed to four substances having the smallest heads and brains and the lowest grey matter volume.
"Although firm conclusions about the discrete individual effects of prenatal cocaine, alcohol or cigarettes on brain volume in the children of our small sample cannot be made, these data are consistent with a possible, lasting effect of each and raise concern that exposure to combinations of these four substances during the prenatal period may have an enduring effect on brain structure in children," Rivkin and his colleagues conclude.
Based on the findings, Rivkin said, health professionals counselling women who are pregnant or thinking of becoming pregnant should warn them not only about the risks of individual substances, but inform them that they could be even riskier in combination.