Government scientists are reporting today that moderate to heavy alcohol consumption during pregnancy can cut off oxygen temporarily to the developing fetus, possibly leading to brain damage.
Although the study was conducted on monkeys, "We suspect that moderate or heavy drinking by pregnant women may have a similiar effect on human fetuses," said Dr. Anil B. Mukherjee of the National Institute of Child Health and Human Development.
His study is one of the first to offer a possible explanation for how alcohol may cause the mental retardation associated with a condition known as "fetal alcohol syndrome."
It also raises concerns, said Mukherjee, about the "cumulative toll" of repeated drinking bouts during pregnancy on the vulnerable fetal brain, which is extremely sensitive to oxygen deprivation.
The scientists conducted their research on monkeys far along in their pregnancies. They were given alcohol until it reached a level in their blood equivalent to that found in humans after a woman had consumed three to five drinks.
Mukherjee and Dr. Gary D. Hodgen, who coauthored research to be published in today's issue of Science Magazine, recommend that women "consider total abstinence" from alcohol throughout pregnancy.
Similiar advice was offered this week from a National Academy of Sciences panel and is supported by Health and Human Services assistant secretary Dr. Edward Brandt.
In the new study, the federal researchers looked at the effects of alcohol in the mother's bloodstream on the function of the umbilical cord, which connects the placenta and the fetus. It delivers oxygen and nutrients from the mother and carries away waste products.
They found, to their surprise, that soon after the five pregnant monkeys in the experiment received injections of an alcohol solution, all of the blood vessels in their umbilical cords collapsed.
The collapses took place within 15 minutes after alcohol administration, with recovery occurring slowly over the following hour.
The doctors said that the "striking interruption" in blood flow had a "markedly adverse" effect on the fetuses, who all developed severe oxygen deficiency and dangerously abnormal blood acidity.
This gradually improved as the umbilical cord function returned. But severe fetal oxygen deprivation "may lead to irreversible brain damage," concluded the National Institutes of Health scientists. They noted that a single brief deprivation "may or may not have discernible consequences."
Adverse effects were not observed in the mothers or in the fetuses of monkeys who received a non-hazardous sugar or salt solution or no injection at all.
All of the monkeys in the experiment were anesthetized and underwent a partial cesarian section that allowed the scientists to observe and measure changes in their infants while they were still in the womb. They found about one-third of the maternal alcohol level in the fetuses, but the alcohol and its byproducts persisted far longer in the developing babies.
"These monkeys are the closest thing you can come to humans. But this kind of experiment could not be done in humans," said Mukherjee. To answer the unsolved questions, he hopes to follow up with experiments involving lower amounts of alcohol that would be orally ingested.
Evidence about the hazards of alcohol during pregnancy has been accumulating in recent years. Initially, attention was focused on chronic alcoholism in the mother, which posed a serious risk of fetal alcohol syndrome in the offspring.
This occurs in about one in 750 infants born in the United States and involves physical changes in the face of the child as well as nervous system problems that may result in mental retardation.
Other studies have shown that drinking as little as 1 to 2 ounces of alcohol daily during the earliest part of pregnancy or single episodes of binge drinking can produce serious changes in growth or development, including possible lingering problems with nervous system impairment.
While much of the concern has been directed at the early stages of pregnancy, when the major organs are developing, the new study suggests that the fetus remains at risk even during late pregnancy.