Single episodes of heavy drinking early in pregnancy may result in serious physical and mental damage to the developing child, a new study at the University of North Carolina suggests.

Based upon animal evidence, researcher Kathleen K. Sulik concluded that there may be a "critical period" soon after conception--roughly equivalent to the third week of pregnancy in humans--in which the developing embryo is particularly susceptible to the condition known as "fetal alcohol syndrome."

"Many women are not aware of their pregnancy at this stage. Those who are may not realize that social or binge drinking so early in pregnancy may be as deleterious to the embryo as constant heavy drinking," write Sulik and her colleagues at the Chapel Hill campus in the current issue of Science magazine.

While fetal alcohol syndrome has previously been associated with chronic drinking by alcoholic mothers, Sulik says her research suggests that women who occasionally get drunk at this early stage of pregnancy, when the embryo is the size of a pinhead and consists of only a few thousand cells, may put the unborn child at added risk.

Fetal alcohol syndrome, which affects an estimated one in 750 births in this country, involves physical changes in the appearance of the child, including a flattened face with small eyes and nose, narrow forehead, and a long upper lip, as well as nervous system problems that may result in mental retardation.

The North Carolina study involved exposure of pregnant mice to two doses of alcohol on the seventh day after conception. Although there was considerable variation, Sulik said yesterday that moderate to severe malformations similar to those found in human fetal alcohol syndrome appeared in as many as 45 percent of the cases.

The blood levels of alcohol involved were equivalent, in human terms, to about twice the legal maximum for drunk driving in most states.

"Women who are social drinkers would not reach this level of intoxication under normal circumstances. If they did, they would be staggering drunk," said Sulik. "However, we don't know yet if lower alcohol levels would be harmful to the embryos of certain individuals.

"Since we don't know safe levels for individuals, I think the best thing to do is not to drink at all," added Sulik, who has a doctorate in anatomy and is the mother of a 1-year-old girl. She noted that she personally does not drink and never has.

While some doctors have simply advised moderation in drinking during pregnancy, the United States surgeon general, Dr. Edward Brandt, recently advised women who are pregnant or considering pregnancy not to drink alcoholic beverages. He noted that some studies had found lower birth weight and greater risk of miscarriage at low levels of alcohol consumption but that fetal alcohol syndrome was generally associated with alcoholic mothers.

Sulik said her animal study was the first to document that subtle birth defects associated with the syndrome may result from "acute" exposure early in pregnancy, although a little-publicized Australian study last year also found that even brief exposure to alcohol could cause other "severe" defects.

A Seattle study in humans also suggested a relationship between alcohol consumption in the month before women knew they were pregnant and the abnormalities associated with fetal alcohol syndrome