If you start out at a healthy weight, that is defined of a BMI of 18.5 to 24.9, you should be gaining an average of 15 to 25 pounds over the course of your pregnancy. And this is average. Everybody is different and as long as you are gaining weight at a steady rate and your OBGYN is okay with the weight gain, you should be fine. If you start out underweight, that is with a BMI of under 18.5, you probably should be getting anywhere between 28 to 40 pounds. If you are a little overweight to begin with, and that is with a BMI of 25 to 29.9, try to gain around 15 to 25 pounds. And if you are obese to start with, with a BMI of over 30, then try to gain around 11 to 20 pounds and no more. If you are having twins and if you are starting off from a healthy weight, try to gain around 37 to 54 pounds.