These guys took into consideration 385 studies published in 1990 or later all focussing on women who gave birth in a hospital. They found that if a woman is not well-nourished during labor, her body will start using fat as an energy source. This causes a whole slew of bad stuff, including an increase in acidity in blood, which leads to reduced contractions, which leads to longer labor and could hurt the baby's health. It's a slippery slope. Better snacking than sorry.
Of course, all women are unique and should consult with a doctor before mowing down those chicken wings in the hospital bed, since individual circumstances could change things. Also, the study suggests a "light snack," so not the time to finish that pot roast.