It is common knowledge that heavy drinking during pregnancy can affect the intelligence of children, but little is known about the effects of light-to-moderate drinking during pregnancy on a child’s IQ.

Now researchers in the U.S. say that for pregnant women, even a few alcoholic beverages per week during the first or second trimester can have harmful consequences on the cognitive development of the unborn child.

Following a long-term study by the University of Pittsburgh School of Medicine and the University of Washington it was found that children who were exposed to between two to six drinks per week during pregnancy, particularly in the second trimester, had a lower IQ compared with children who were not exposed to alcohol while in the womb.

Lead study author Dr. Jennifer A. Willford an experimental psychologist at the University of Pittsburgh says that IQ is a measure of the child’s potential to learn and survive in his or her environment and predicts how successful a child will be in school, work and life.

Willford says the results of the study show that low-to-moderate levels of prenatal alcohol exposure have a sustained negative effect on a child’s IQ.

The team examined data from 636 mother-child pairs who attended a prenatal clinic from 1983 to 1985 where the women provided information on alcohol use during each trimester of pregnancy; their child’s cognitive ability was assessed at age 10 on the basis of verbal, quantitative, and short-term memory tests.

The researchers found that in African-American 10-year-olds, low-to-moderate alcohol exposure in the first and second trimesters significantly predicted deficits in the composite score of a standard test of intelligence, as well as several individual components of the test.

However in Caucasian children in the study no such link was found and Willford says that neither racial difference or socioeconomic factors could explain the difference but it was more prominent among African-American children compared to Caucasian children.

The investigators also found that binge drinking was not the best predictor of future cognitive defects in children whose mothers drank at light-to-moderate levels during pregnancy but the overall amount of alcohol consumed during pregnancy was more likely to predict whether or not a child’s cognitive development would be impaired.

Willford says that although a small but significant percentage of children are diagnosed with Fetal Alcohol Syndrome each year, many more children are exposed to alcohol during pregnancy who do not meet criteria for FAS yet experience deficits in growth and cognitive function.

The research is published in the journal Alcoholism: Clinical and Experimental Research, June 2006.