The growing fetus develops in a warm and watery world. The womb is a cozy and stable environment, but it is rich in auditory stimuli: the sounds of the mother’s heart beat, digestive rumblings, and the soft whoosh of blood flow. Most of these sounds are patterned and rhythmic. Sounds from outside of the woman’s body, such as voices and music, also reach the fetus, but they are muted. The auditory system of the fetus is mature at roughly 20 weeks, and researchers have shown that the fetus can actually hear at 24-25 weeks. The fetus is also preparing for her own addition to the acoustic environment.
At 11 weeks, the vocal cords of the larynx—the voice box—begin to form, even though the fetus will have to wait another 6 months to power this instrument with her first gulp of air. It might be surprising that fetal eyes begin to develop so early, given the darkness of the womb, but by week 4, the developing eye is present as a tiny dot, and by week 6, the eye is distinct. Eyelids start developing at the same time, but by week 8, the eyelids start closing up and completely close up around 9 weeks. They reopen around week 26. Visual MD
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