While researchers have found that heavy drinking during pregnancy leads to lower intelligence in children, fewer studies have focused on the effects of light-to-moderate levels of alcohol exposure. This study found that in 10-year-old African-Americans, exposure to between two and six drinks per week during pregnancy, especially in the second trimester, was associated with a lower IQ score compared to children who were not exposed to alcohol prenatally. There was no association found in Caucasian children.
"IQ is a measure of the child's potential to learn and survive in his or her environment. It predicts how successful we will be in school, work and life," said Jennifer A. Willford, Ph.D., assistant professor of psychiatry, University of Pittsburgh School of Medicine, and lead author of the study. "If light-to-moderate drinking can lower IQ, it suggests that mothers should try to abstain during their pregnancies to prevent their children from having cognitive deficits."
Interestingly, the study also revealed that binge drinking was not the best predictor of future cognitive deficits in children whose mothers drank at light-to-moderate levels of alcohol during pregnancy. The overall level of exposure over time was more important in predicting the effect alcohol would have on the child.
This study used data from the Maternal Health Practices and Child Development Project, an examination of prenatal substance abuse in women who attended a prenatal clinic from 1983 to 1985 in which women were assessed during each trimester of pregnancy, and again with their children at birth, eight months, 18 months, and at three, six, 10, 14, 16, and 21 years of age. At 10 years of age, the children's cognitive ability was assessed using the Stanford Binet Intelligence Test.
After normalizing the data to account for factors also known to predict cognitive ability, including maternal intellectual ability, maternal drug use, psychosocial characteristics, socioeconomic status and home environment, researchers were able to understand how prenatal alcohol exposure lowered IQ within the context of other risk factors that might lead to cognitive deficits. They found a relationship between low-to-moderate alcohol exposure during the first and second trimester and intelligence at age 10 in African-American children, but no relationship in Caucasian children.
"Our results indicate that the differences in prenatal alcohol effects on the IQ scores of African-American and Caucasian children were not due to the amount or pattern of drinking during pregnancy, their socio-economic status, or the education levels of the parents. We cannot say why this racial difference exists, but other laboratory animal and human studies suggest that genetics may play a role," said Dr. Willford.
"Regardless, the results show that alcohol exposure has a sustained negative effect on the child. We suggest that women speak with their obstetricians about drinking when they are planning a pregnancy or when they learn that they are pregnant. Many women know about fetal alcohol syndrome and the effects of heavy drinking. However, studies are showing that even light-to-moderate levels of drinking during pregnancy also can be harmful. Since none of the studies has suggested a 'safe' level of alcohol exposure during pregnancy, we can only say it's safer not to drink at all," said Dr. Willford.
Co-authors of the study are Sharon L. Leech, M.P.H. of the University of Pittsburgh Medical Center, and Nancy L. Day, Ph.D., professor of psychiatry, University of Pittsburgh School of Medicine.
The study was funded through grants from the National Institute of Alcoholism and Alcohol Abuse and National Institute on Drug Abuse.