The guidelines for pregnancy weight gain are issued by the Institute of Medicine (IOM) in May 2009. Here are the most current recommendations:
If your pre-pregnancy weight was in the healthy range for your height (a BMI of 18.5 to 24.9), you should gain between 25 and 35 pounds, gaining 1 to 5 pounds in the first trimester and about 1 pound per week for the rest of your pregnancy for the optimal growth of your baby.
If you were underweight for your height at conception (a BMI below 18.5), you should gain 28 to 40 pounds.
If you were overweight for your height (a BMI of 25 to 29.9), you should gain 15 to 25 pounds. If you were obese (a BMI of 30 or higher), you should gain between 11 and 20 pounds.
If you're having twins, you should gain 37 to 54 pounds if you started at a healthy weight, 31 to 50 pounds if you were overweight, and 25 to 42 pounds if you were obese.
Use a pregnancy weight gain estimator to find out how much you should gain (based on your height and pre-pregnancy weight) and to see how the pounds are distributed.