At this time, the main purpose of an ultrasound examination is to assess the condition of the placenta, the quantity and quality of amniotic fluid, the location of the fetus, and the calculation of child's weight and height. Usually by this time the baby is situated with its head down and the buttocks up - this is the most comfortable position for delivery of the fetus. The aging process is beginning in the placenta. But despite an active process of aging, the placenta still performs its main role. The baby is closely surrounded by amniotic fluid; its movements are limited and constrained.