You should gain during your pregnancy. If you're underweight, try to gain 28-40 pounds. Normal weight? Shoot for 25-35 pounds. Overweight? Gain 15-25 If you're obese, try to put on 11-20 pounds. Expecting twins or multiples? Your goal weight goes up. Gain 50-62 pounds if you're underweight. 37-54 if you started at a normal weight. 31-50 if you're overweight. And 25-42 if you're obese. When you're pregnant with one baby, get about 300 extra calories per day starting in your 2nd trimester. You'll need more than that if you're having twins or multiples, so check with your doctor. Put on the extra pounds slowly and steadily.