Usually when everything is normal, the baby moves on average 50 times an hour, has a body of up to 17 to 18.5 centimeters and weighs about 298 grams or so. At 21 weeks, the baby’s brain is undergoing rapid development, and the hippocampus of the brain, which is responsible for memory as well as spatial localization functions, is beginning to develop. The fetus is able to absorb water from the amniotic fluid in addition to swallowing it. During the 21st week of pregnancy, the mother will experience a significant protrusion of the lower abdomen, a relatively rapid rate of weight gain, and will feel pain in the lower back. The protruding abdomen will cause the mother’s center of gravity to shift forward, making her movements slow, while the enlarged uterus will also press on the surrounding organs. Mothers are advised to have regular checkups, eat a proper diet and take rest.