Dr. Ron Gray of the University of Oxford and colleagues at the University of Bristol used data involving more than 4,000 mothers and their children in the Children of the 90s study -- which tracks health and development of the parents and their children over a generation.
The study, published in the journal PLOS ONE, found four genetic variants in alcohol-metabolizing genes among the 4,167 children were strongly related to lower IQ at age 8. The child's IQ was on average almost 2 points lower per genetic modification they possessed.
This effect was seen only among the children of women who were moderate drinkers. There was no effect evident among children whose mothers abstained from alcohol during pregnancy, strongly suggesting it was the exposure to alcohol in the womb that led to the difference in child IQ. Heavy drinkers were not included in the study, Gray said.
"This is a complex study but the message is simple: Even moderate amounts of alcohol during pregnancy can have an effect on future child intelligence," Gray, the study leader, said in a statement. "So women have good reason to choose to avoid alcohol when pregnant."