TUESDAY, Jan. 15, 2002 (HealthDayNews) -- Drinking during pregnancy may cause birth defects because neither the mother nor her baby get enough of the hormone necessary for fetal growth, a new sheep study suggests.
"It's possible that alcohol may suppress thyroid function of both the mother and the baby -- the mother, beginning right from the start of the pregnancy, and the baby, later on, as their thyroid gland develops," says study author Dr. Timothy A. Cudd, associate professor of physiology at Texas A&M University.
Cudd points out that the birth defects seen in children born to mothers with low thyroid function appeared to mimic those seen in children born to mothers who drink during pregnancy.
Putting the two ideas together, Cudd theorized that alcohol's effect on the thyroid was behind alcohol-related birth defects.
"We felt it was possible that alcohol was affecting the thyroid of both mother and baby, and that, in turn, was causing the birth defects normally attributed to alcohol," says Cudd.
For Dr. Lynn Simpson, the theory sheds new light on a complex topic.
"Right now, we don't know why or how alcohol consumption during pregnancy affects the fetus -- and what's more, we don't know why it only affects some babies and not others," says Simpson, associate professor of obstetrics and gynecology at Columbia University College of Physicians and Surgeons.
Clearly, she says, there must be another factor at work along with the alcohol -- and it's possible that low thyroid function could be the compounding factor.
Thyroid hormone is essential for growth and development of numerous hormone and organ systems in a developing baby. Early in the pregnancy, all the thyroid hormone comes from the mother, so if the supply is low, baby is shortchanged from the start, says Cudd.
More importantly, as a baby develops, higher levels of thyroid hormone are required, so the baby's own developing supply must help create concentrations sufficient for healthy growth and development.
"If the alcohol is affecting the mother's thyroid, it's also affecting the fetus's thyroid, so neither one is producing enough hormone necessary for proper growth and development," says Cudd.
Previous studies have shown children born to mothers with low thyroid function score less well on tests designed to measure intelligence, attention, language, reading ability, and school performance, when compared to children whose mothers' thyroids functioned normally during pregnancy.
To test his theory on alcohol-mediated thyroid function, Cudd's team relied on a group of pregnant sheep -- chosen because their cycle of fetal development mimics that of a human fetus.
Beginning on the 109th day of their pregnancy -- equal to the start of the third trimester in humans -- each of the sheep began receiving either saline solution or alcohol. Those assigned to get the alcohol received doses that equaled about two glasses of wine consumed by a 120-pound pregnant woman up to a dose that correlated to about nine glasses of wine.
To simulate binge drinking, the animals received the alcohol every day for three days, followed by four days of abstinence. The cycle continued through the remainder of the pregnancy. For sheep, total gestation time is usually about 145 days.
During the testing period, fetal and maternal blood samples of thyroid hormone and other factors were collected on days 118 or 132.
In those sheep that were given the alcohol, tests showed thyroid function was low -- meaning the fetus did not receive enough of the hormone necessary for proper growth and development. Subsequent biopsies on the sheep fetuses confirmed the finding.
The study was published in the January issue of the journal Alcoholism: Clinical & Experimental Research.
Simpson says the research is significant because "we just do not understand how alcohol exerts its negative effects on the developing fetus."
This research, she says, introduces a potential mechanism that may lead to some effective treatment.
Right now, says Simpson, "the important message at this point in time is that the minimum amount of alcohol that can cause fetal problems is unknown and until further data is available, alcohol should be avoided during pregnancy."
Cudd agrees. "If our study proves true, then it may be possible to monitor thyroid hormone throughout a pregnancy, and correct any imbalance as it occurs," he says. "And this might then mitigate the effects of alcohol on the fetus."
What To Do
For more information on fetal alcohol syndrome, visit Medicinenet.com.
For a quick fact sheet on why pregnancy and alcohol don't mix, visit the American Academy of Family Physicians.
To learn more about how thyroid disorders affect pregnancy, go to Colorado State University.
