•In the average woman, weight gain is considered excessive if it is more than 3 kg (6.6 lbs) a month during the second and third trimesters. It is unusual if it is under 1 kg (2.2 lb) per month during the second and third trimesters. Therefore the answer is 1 lb per week.
•A weight gain of 25 to 35 pounds is currently recommended as an average weight gain in pregnancy. Weight gain in pregnancy occurs from both fetal growth and accumulation of maternal stores.
•Women who are underweight coming into pregnancy should gain slightly more weight, while an obese woman might be advised to gain less than average.