The Changing Rules of Parenthood

Pregnancy Best Practices

Then: Limit pregnancy weight gain to 15 to 20 pounds. (Good luck with that!)

Now: A woman with a normal pre-pregnancy weight should gain between 25 and 35 pounds.

Why: "In the old days, they said women shouldn't gain any more than the weight of the baby and the weight of the placenta combined," says Dr. Paul Peebles, a Bethesda, Maryland-based pediatrician in practice for 40 years and author of Oh, My Gosh, We're Pregnant.

Now we know that women who don't gain enough weight during pregnancy are more likely to have underweight babies. These days, the average healthy weight gain is considered to be four to six pounds for the first 12 weeks of pregnancy, and about a pound a week after the first trimester. But even though you can shelve the diet books for now, you shouldn't use pregnancy as an excuse to pig out—make sure you stock up on healthy foods.