If you are of average weight before pregnancy, you should almost certainly gain between 20 and 35 pounds. This weight gain involves the growing baby, as well as many of the changes your body go through to support the baby. The breakdown normally looks something like this:

Baby 6 to 9 pounds

Placenta 1 to 2 pounds

Uterus 2 pounds

Amniotic fluid 2 to 3 pounds

Added breast weight 1 to 2 pounds

Added blood volume 2 to 3 pounds

Added tissue fluid 4 to 6 pounds

Fat 5 to 8 pounds

Total weight gain 23 to 35 pounds

If you were underweight or overweight before pregnancy, you may benefit from gaining more or less than the recommendations for women of normal weight. Eventually, the quality of your diet is more influential than the number of pounds you gain during pregnancy.