The vestibular system, designed to register head and body motion as well as the pull of gravity begins developing at about 8 weeks. This requires construction of six semicircular canals, fluid-filled structures in the ears, which are sensitive to angular acceleration and deceleration, and help maintain balance. Tasting and Smelling The structures for tasting are available at about 14 weeks g.a. and experts believe that tasting begins at that time. Tests show that swallowing increases with sweet tastes and decreases with bitter and sour tastes. In the liquid womb space, a range of tastes are presented including lactic, pyruvic, and citric acids, creatinine, urea, amino acids, proteins and salts.
Tests made at birth reveal exquisite taste discrimination and definite preferences.
Until recently, no serious consideration was given to the possibilities for olfaction in utero, since researchers assumed smelling depended on air and breathing. However, the latest research has opened up a new world of possibilities. The nose develops between 11 and 15 weeks. Many chemical compounds can cross the placenta to join the amniotic fluid, providing the fetus with tastes and odors. Associations formed in utero can alter subsequent fetal behavior and are retained into postnatal life.