Your Metabolism Increases

What happens: A surge of hormones -- such as human placental lactogen (HPL) -- changes the way your body processes energy, stores fat, and delivers nutrients to your baby.

Why it happens: You need extra energy to grow another human. But before you put "Burritos R Us" on speed dial, be aware that the boost doesn't exactly translate to "eating for 2." In fact, a more accurate guideline is "eating for 1.1." Essentially, when you're pregnant, you need to eat only 10% more than the number of calories you ordinarily eat.