The average recommended weight gain for women of normal pregnancy weight is 25 to 35 pounds; underweight women should gain a little more than this and overweight and obese women should gain somewhat less. Women who are pregnant with twins are advised to gain 37 to 54 pounds.
Women who gain too little weight during pregnancy increase their risk of having a preterm or low-birth-weight baby and depleting their own nutrient reserves. Gaining too much weight during pregnancy increases the risk of trauma during delivery. Also children born to overweight or obese mothers have higher rates of childhood obesity and metabolic syndrome.
The pattern of weight gain is what is also important. During the first trimester, a woman of normal weight should gain no more than 3 to 5 pounds. During the second and third trimester, an average of about 1 pound a week is considered healthful for normal weight women. For overweight women, a gain of 0.6 pounds per week is appropriate. If weight gain is excessive in a single week, month or trimester, the woman shouldn’t attempt to diet or lose weight because it can be harmful to the health of the mother and fetus by depriving them of important nutrients. The newborns of women who lose weight during the first trimester due to severe nausea or vomiting are likely to be lower birth weight than women with appropriate weight gain. Weight gain through pregnancy should be slow and steady.
Source: Thompson, Janice, Melinda Manore, and Linda A. Vaughan. The Science of Nutrition. San Francisco, CA: Pearson Benjamin Cummings, 2011. Print.