A new study suggests that a mother's substance use during pregnancy, especially a combination of substances, may result in a smaller brain for her child, Reuters reported April 14.

The study observed 35 children 10 to 14 years old whose mothers had used cocaine, drank alcohol, or smoked tobacco or marijuana during pregnancy.

Magnetic resonance imaging was used to measure the volume of different types of brain tissue in the study participants. Researchers also measured head circumference.

Although fetal exposure to a single substance did not show statistically significant impacts, a combination of two substances produced significant reductions in the three measures of brain size and a smaller head circumference than those of peers who weren't exposed prenatally to these substances. Brain size reductions were greater still in children exposed to four substances.

"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," said Dr. Michael J. Rivkin of Children's Hospital and Harvard Medical School in Boston.

Rivkin suggests that pregnant women or women considering pregnancy should be counseled about the risks of individual substance use and the even greater risks of using multiple substances.