There may be a "safe" amount, but research has not been able to identify what amount that might be. According to The American Academy of Pediatrics:
Mills et al14 prospectively studied approximately 31 000 pregnancies in an attempt to determine how much alcohol pregnant women can consume safely. The consumption of 1 or more drinks (a drink is defined as 1.5 oz distilled spirits, 5 oz of wine, or 12 oz of beer) per day was associated with increased risk of giving birth to an infant with growth retardation. Although maternal age, parity, and health as well as specific fetal susceptibility may contribute to the infant's outcome, the potential for harm to the fetus is much stronger with large amounts of maternal alcohol consumption than with smaller amounts.15 Nevertheless, current data do not support the concept of a "safe level" of alcohol consumption by pregnant women below which no damage to a fetus will occur.
The AAP's official recommendation states:
Because there is no known safe amount of alcohol consumption during pregnancy, the Academy recommends abstinence from alcohol for women who are pregnant or who are planning a pregnancy.
From the March of Dimes website:
No level of drinking alcohol has been proven safe during pregnancy. According to the U.S. Surgeon General, the patterns of drinking that place a baby at greatest risk for FASDs are binge drinking and drinking seven or more drinks per week (7). However, FASDs can occur in babies of women who drink less.
Researchers are taking a closer look at the more subtle effects of moderate and light drinking during pregnancy.
- A 2002 study found that 14-year-old children whose mothers drank as little as one drink a week were significantly shorter and leaner and had a smaller head circumference (a possible indicator of brain size) than children of women who did not drink at all (8).
- A 2001 study found that 6- and 7-year-old children of mothers who had as little as one drink a week during pregnancy were more likely than children of non-drinkers to have behavior problems, such as aggressive and delinquent behaviors. These researchers found that children whose mothers drank any alcohol during pregnancy were more than three times as likely as unexposed children to demonstrate delinquent behaviors (9).
- A 2007 study suggested that female children of women who drank less than one drink a week were more likely to have behavioral and emotional problems at 4 and 8 years of age. The study also suggested similar effects in boys, but at higher levels of drinking (10).
- Other studies report behavioral and learning problems in children exposed to moderate drinking during pregnancy, including attention and memory problems, hyperactivity, impulsivity, poor social and communication skills, psychiatric problems (including mood disorders) and alcohol and drug use (2).
In short, while there's no evidence of causation between light drinking during pregnancy and problems, there are studies that suggest a correlation between even light drinking and various problems. The correlation with serious health risks increases as the amount consumed increases, but there has not been a "safe" amount consistently identified, likely due to variations in individual metabolisms and how the alcohol is processed by the mothers' bodies.