The sense of hearing develops first among five senses. Within a few days of fertilization in the mother, the fertilized egg begins to shape the ear when it is only 0.9 mm in size. In the third week of pregnancy, the inner ear (internal ear)1 develops, and the cochlea is differentiated in six weeks and connected to nerve cells in about 20 to 24 weeks. This means that the fetus can hear sounds.
1. The inner most part of the ear, surrounded by hard bones. It consists of the cochlea, vestibule, and semicircular canals, and transmits vibrations of the eardrum to nerves.
The fetus becomes able to hear while other organs have not yet grown, and emotions develop through the sound and the brain grows. Prenatal education too is to stimulate the sense of hearing; the fetus’s favorite is definitely the mother’s voice. External sounds diminish as they pass through the amniotic fluid, but the mother’s voice is amplified while passing through the spine to the pelvis. The fetus remembers the mother’s voice and distinguishes it from others’. A newborn baby who can’t even open his eyes responds to his mother’s voice because he remembers it.
Although the fetus can’t see his or her mother, it can hear her voice by ear. The reason hearing develops earlier than other senses may be to feel the mother who conceives it through the voice.