This beautiful photo of a fetus at 19 weeks shows this baby sucking the thumb surrounded by the transparent membranes of the amniotic sac.

Photo: © Bromhall / Photo Researchers, Inc 2006



Baby Aerobics. In the second trimester, the fetal skeleton continues to produce more bone. The boys can bend their arms at the elbow and wrist and make a fist. At this point, however, these movements are purely reflexive and are not controlled by the brain. By week twenty-two, baby can react to loud noises and music! We don’t know if this represents exercise, but it is fun to think of them as doing baby aerobics inside the uterus. The baby will have alternating periods of sleep and wakefulness, and a tap on mother’s abdomen can awaken a sleeping fetus.

Breathing Practice. The boys can move amniotic fluid into and out of the lungs, about a pint a day it is thought, and excretes a similar amount through fetal urine. True gas exchange will not occur until the air sacs of the lungs expand. This expansion cannot take place until a baby takes its first breath. Swallowing and breathing require complex coordination between the nerves and muscles. It is truly an amazing process!