Have you ever heard—or noticed yourself—that a fetus can respond with a kick to loud noises from outside the womb? It's true—and scientists even suspect it can recognize familiar sounds, particularly its mother’s voice. This is due at least in part to the fact that the auditory system is highly developed early on. "Hearing is the most sensitive of all senses at birth," says Kenneth Lyons Jones, M.D., a professor of pediatrics at the University of California, San Diego.
You'll notice this from day one if your newborn hears a loud noise—he’ll undoubtedly startle. What he won't be able to do is turn toward a noise; that happens a bit down the road. "A baby will begin to turn his head toward a familiar sound, particularly his mother's voice, within the first month," Jones says. "This is very important and something you should watch for."
While some developmental milestones are not crucial in terms of when they are mastered, responding to sounds is. That's because it’'s tied so closely to hearing. "If a child is not walking until 14 months, maybe even a bit later, that’s OK," Jones says, "but if he's not hearing, that’s really important."
"Speech is totally dependent on hearing," he explains, "so this is a critical issue."
While your newborn may have had a hearing screening test in the hospital, as many states now mandate, it's still important to watch for signs that he’s hearing properly. "If at the end of the first month your baby’s not turning toward your voice, bring it to your pediatrician's attention right away," Jones says.