Average Pregnancy Weight Gain Distribution. 1  7 1/2 pounds is about how much the baby will weigh by the end of pregnancy. 2  1 1/2 pounds is how much the placenta weighs. 3  4 pounds is attributed to increased fluid volume. 4  2 pounds is the weight of the uterus. 5  2 pounds is the weight of breast tissue. 6  4 pounds is because of increased blood volume.