What is a health weight gain at 31 weeks?

Depends: If you start out the pregnancy at your ideal body weight then you can expect to gain about 20-30 pounds during the pregnancy. However if you are overweight or obese at the start of your pregnancy then you may want to keep your weight steady throughout the pregnancy by eating very healthy and exercising regularly.

20-25 pounds: A normal weight gain for a 40 week pregnancy is in the 25-35 pound range. Women who weigh less at the onset of pregnancy will benefit more from a greater weight gain than those who weight more at the onset. At around 30 weeks most women will have gained about 25 pounds.