Moreover, definitions of light, moderate and heavy drinking can
vary enormously. Investigators who consider light drinking to be
up to a drink a day tend to conclude that the practice is more
harmful than those who say light drinking means up to one drink
a week. (The alcohol content in “one drink” can also differ.)
And many studies are based on an “average” number of drinks per
time interval, which can lump together dramatically different
drinking patterns—for example, imbibing one a week and bingeing
on five in one night in a month. And yet, Day says, “there's a
lot of literature that shows that binge drinking may have a
bigger effect.” One 2009 study, for example, tied a single binge
during pregnancy to hyperactivity and attention problems in
children. Most studies of periodic light drinking, on the other
hand, find that it has no effects. Teasing Out the Truth Because
individual studies so often conflict, coming to a consensus
about how much alcohol—if any—is safe for an expectant mother is
a tall order.