Weight gain during pregnancy should be gradual with the most weight being gained in the last trimester. According to the ACOG, you should gain about 2 to 4 pounds during the first three months of pregnancy and then 3 to 4 pounds per month for the rest of your pregnancy. Total weight gain should be about 25 to 30 pounds. This will decrease the risk of delivering a low-birth-weight baby. The Institute of Medicine recommends that women who have a low Body Mass Index (BMI) — the ration of weight to height — should gain 28 to 40 pounds during pregnancy and women who have a higher BMI should gain 15 to 25 pounds. Check with your doctor to determine how much weight gain during pregnancy is healthy for you.