Fetuses exposed to heavy binge drinking required significantly more time to habituate, or adjust, to repeated stimulation in the womb and also showed greater variability in test performance, according to a new study.
This study is the first of its kind, examining alcohol’s effects on fetal brain function — information processing and stability of performance — right at the moment a fetus is exposed to alcohol.
“This study used a process of habituation, which is the ability of an organism to stop responding to repeated stimulation,” explained Leo Leader, M.D., a senior lecturer in the School of Women’s and Children’s Health at the University of New South Wales.
“This reflects the ability of the central nervous system to learn to recognize a particular stimulus. It is widely accepted that habituation represents a basic form of learning.
Previous research has shown that the normal human fetus habituates, but habituation rates are altered if the fetus is exposed to reduced oxygen levels, maternal smoking, maternal sedatives, and impaired fetal growth.”
Most studies that examine the effects of fetal brain behavior are conducted during the postnatal period.
“When examined after birth, individuals who have been prenatally exposed to alcohol exhibit a wide range of behaviors that are indicative of central nervous system dysfunction,” said Peter G. Hepper, Ph.D., a professor of psychology at Queen’s University of Belfast as well as corresponding author for the study.
“These can include poorer abilities to learn, deficits in attention, poorer abilities to plan and organize, and an inability to learn about the consequences of actions. As a consequence, they may demonstrate behavioral difficulties and social problems which might lead to problems at school, and often ‘trouble with the law.'”
For the study, Hepper and his colleagues examined 78 non-smoking mothers with normal, apparently healthy, single pregnancies from the Royal Jubilee Maternity Service in Belfast. Researchers played a loud two-second sound to the fetus via a speaker on the mother’s abdomen. Using ultrasound, they watched whether the fetus moved, jumped or startled to the sound.
The sound was repeated every five seconds and the response of the fetus recorded each time. As the sounds were repeated, the fetus’s response got weaker and eventually, after a number of sound presentations, disappeared. At this point the fetus is said to have habituated, according to Hepper.
“We have demonstrated that at the time of exposure, alcohol is affecting a fundamental psychological process known as habituation that underlies many of our more complex psychological abilities,” said Hepper.
Results showed that the fetuses of mothers who binge drink five to 10 drinks per week, or drink more than 20 drinks a week, or as a binge over two to three days take far longer to habituate.
“The study also showed that binge drinking was associated with more variability of the fetus to learn. For normal learning and development, the fetal brain requires stability and this result implies that binge drinking impaired this function,” said Leader.
Both Hepper and Leader noted that no safe level of alcohol consumption during pregnancy has been identified.
“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. By observing the behavior of the fetus it will be possible to ascertain which and by how much individuals have been affected by exposure to alcohol.
“To be safe, however, no drinking during pregnancy would be wise.”
Results will be published in the December 2012 issue of Alcoholism: Clinical & Experimental Research.