According to American College of Obstetrics and Gynecology the recommended weight gain for singleton pregnancy is 25-35 pounds during a singleton pregnancy. Maternal weight gain during pregnancy could be due to: Fetus: 3500 gm at term Placenta: 650g Amniotic fluid:800mg Breast enlargement: 400g Uterus: 970g Interstitial fluid and blood volume: 1200-1800 gm. Underweight women should gain more weight of 12.5-18 kg or 28-40 lb. Obese women should gain less than 7-11.5 kg or 15-25 lbs. Ref: Bernstein H.B., VanBuren G. (2013). Chapter 6. Normal Pregnancy and Prenatal Care. In A.H. DeCherney, L. Nathan, N. Laufer, A.S. Roman (Eds),CURRENT Diagnosis & Treatment: Obstetrics & Gynecology, 11e.