Alcohol Slows Unborn Babies' Learning

Alcohol during pregnancy reduces learning speed of babies while they are still in the womb

/ Author:  / Reviewed by: Robert Carlson, M.D

(RxWiki News) Many studies have looked at differences in children whose mothers drank while pregnant compared to kids whose moms didn't. But what about differences before the babies are even born?

A recent study has found differences in basic learning among unborn children based on how much their mothers drink.

"Don't drink alcohol while pregnant."

The study, led by Peter G. Hepper, PhD, of the School of Psychology at Queen's University in Belfast, Northern Ireland, focused on the impact of alcohol on a process called "habituation" while a baby is still in the womb.

Habituation occurs when someone stops responding to a certain stimulus because it happens over and over.

Habituation is a type of basic learning because it shows that the central nervous system can recognize the stimulus.

Dr. Hepper and his colleagues wanted to see how habituation in an unborn child was affected by the mother's alcohol intake.

Past research has studied habituation in the womb and seen it reduced in fetuses when their oxygen levels are low, women smoke or take sedatives or when the fetus is not growing properly.

For this study, the researchers studied five groups of 78 unborn babies, divided according to how much and how often their mothers drank alcohol.

The groups were similar in terms of how many children the women already had, the women's ages, any pregnancy complications they experienced, how they delivered their babies, the week of pregnancy when they delivered, their babies' genders and birth weights and their babies' Apgar score five minutes after birth.

One group of 30 pregnant women drank no alcohol, and two groups were "moderate" drinkers.

"Moderate" was defined as five to ten drinks spread across a week in one group of 15 women and as five to ten drinks in a binge over two to three days for the other group of 13 women.

The final two groups were "heavy" drinkers, one, with 9 women, having more than 20 drinks throughout a week and the other, with 11 women, having over 20 drinks during a binge.

The stimulus used in the study was a loud two-second sound played out of a speaker held at the woman's abdomen.

The researchers watched the fetus on an ultrasound monitor to see if the baby moved or jumped at the sound.

As they played the sound every five seconds, the baby's reaction to each sound was noted, becoming weaker and weaker as the baby habituated to the sound.

Once the baby no longer moved or jumped at all from the sound, it had become habituated.

The researchers tested the babies' habituation three times, a week apart, starting when the mothers were in their 35th week of pregnancy.

The results showed that babies of the "moderate" binge-drinking mothers and of both the heavy drinking groups took longer to habituate to the sounds.

The habituation occurred at about the same rates for the women who binge drank moderately and those who drank heavily throughout the week.

"Maternal drinking, either heavily but evenly or moderately as a binge, resulted in poorer habituation, and moderate binge drinking resulted in greater variability compared with no, or even, drinking," the authors concluded.

"For normal learning and development, the fetal brain requires stability and this result implies that binge drinking impaired this function," Dr. Hepper said.

The researchers theorized that alcohol exposure to the fetuses may be causing structural damage to the brain that reduces the ability of the baby to process information.

No significant differences in habituation rates were found between the women who didn't drink and the women who drank five to ten drinks spread out across a week.

However, the researchers emphasized that there is currently no known "safe" level of drinking during pregnancy that has been established.

"One 'oddity' of prenatal exposure to alcohol is there are large individual differences in its effects," said Hepper. "Some individuals whose mothers drink heavily may exhibit few effects whilst others whose mothers drink less may exhibit much greater effects.

The study was published September 14 in Alcoholism: Clinical & Experimental Research. The research was funded by a grant from Northern Ireland's Department of Health and Social Services and Public Safety and a grant from the National Institute on Alcohol and Alcohol Abuse.

Reviewed by: 
Review Date: 
September 13, 2012
Last Updated:
September 17, 2012