Is it safe to drink diet soda during pregnancy?

DEAR DOCTOR K: My beverage of choice is diet soda, but my girlfriend told me I should stop drinking it now that I'm pregnant. Is she right?
DEAR READER: For some time now, research has shown that when pregnant women gain a lot of weight during pregnancy, they have heavier babies. Heavier babies tend to grow into heavier children, who tend to grow into heavier adults. And being overweight or obese in childhood can adversely affect a child's future health and well-being. So it's a good idea for pregnant women to try not to gain more than their doctors tell them to.