TUESDAY, June 19 (HealthDay News) -- One of the cardinal rules for expectant moms: don't drink.

But a new study out of Denmark is throwing that maxim into doubt. It finds that 5-year-olds whose mothers drank low to moderate levels of alcohol (between one and eight drinks a week) during early pregnancy showed no ill effects.

Alcohol consumption during pregnancy that exceeded the "moderate" threshold, however, was associated with a lower attention span among children in that age group.

Despite the findings, experts who reviewed the research said it shouldn't change standard recommendations.

"These findings can easily send a very dangerous message to pregnant women," said Bruce Goldman, director of Substance Abuse Services at the Zucker Hillside Hospital in Glen Oaks, N.Y. He noted that the U.S. surgeon general advises against drinking during pregnancy to avoid fetal alcohol spectrum disorders.

"Women may underestimate and have difficulty acknowledging the frequency or quantity of alcohol consumed," Goldman said. "Those suffering from alcoholism may attempt to rationalize that it is safe to drink moderately, something they may ultimately be unable to do."

In the study, researchers analyzed data from more than 1,600 women in the Danish National Birth Cohort. The amount of alcohol consumed by the women during their pregnancy was classified as either none, low (one to four drinks per week), moderate (five to eight drinks per week) or high (nine or more drinks per week). Binge drinking was defined as having five or more drinks on a single occasion.

At age 5, the women's children underwent tests to assess their IQ, attention span and thinking skills needed for planning, organization and self-control.

Overall, low to moderate weekly drinking during pregnancy had no significant effect on the children's brain development, the team reported. Nor did binge drinking. There was, however, a link between high levels of drinking during pregnancy and lower attention spans in offspring at age 5.

The findings appear in five different studies published June 20 in BJOG: An International Journal of Obstetrics and Gynecology.

Although it's still best for pregnant women to avoid alcohol, these results suggest that small amounts may not be a serious concern, concluded researchers led by Ulrik Schioler Kesmodel, a consultant gynecologist and associate professor at Aarhus University and Aarhus University Hospital.

They called, however, for more large-scale studies to further investigate the possible effects of low to moderate alcohol consumption during pregnancy.

Another U.S. expert familiar with the findings said it's still too early to give women a pass to drink while pregnant.

"I would still caution women about drinking during their pregnancies," said Dr. Jennifer Wu, an obstetrician/gynecologist at Lenox Hill Hospital in New York City. "There may be subtle neurobehavioral changes that were not picked up in the study."

"Also, it can be hard to accurately test younger children," she said, and "tests at an older age may detect larger differences."

More information

The U.S. Centers for Disease Control and Prevention has more about alcohol and pregnancy.