Nature does a pretty good job of programming or presenting the necessary kinds of stimulation that a fetus should get at the appropriate times during development," says William Fifer, a developmental psychobiologist at Columbia University. In fact, experts worry that sticking speakers or headphones up to your abdomen could actually disrupt your baby's sleep patterns or the natural order of growth.
If there's any benefit to spending time talking to your baby or letting your favorite music filter naturally through the uterine wall, it's as much for the parents as for the baby, they say. "I think most of the purpose of talking to your baby is to give people a chance to sort of attach, to get used to the fact that this new creature is going to be a big part of your life," says Fifer. Your baby's hearing is intact by the third trimester, when sonograms show that a fetus will actually turn its head to respond to a sound. But studies have shown that your unborn child can hear sounds as early as 20 weeks and will be startled by loud noises at about 25 weeks. Very loud sounds can cause changes in your baby's heart rate and movements, and sometimes even cause them to empty their bladders.
Instead of the womb being the quiet place scientists once assumed, it is actually awash in sounds, particularly the whooshing of your blood and digestive system, the thumping of your heart and your voice, which sounds louder than it would transmitted through the air since it reverberates through the bones and fluids in your body. Noises from outside your body are more muffled but they also make it through surprisingly clearly, says Robert Abrams, a fetal physiologist in the department of obstetrics and gynecology at University of Florida. Low frequency sounds, such as those above middle C, tend to be more audible than higher frequency ones. Men's voices, for instance, come through clearer than women's, and music also is easily recognizable.
It appears the fetus can even hear specific speech patterns and intonations, although probably not recognize words themselves, Fifer says. Some studies have shown that babies after birth will recognize -- and be comforted by -- a story read repeatedly to them while in the womb or even by particular songs, like the theme from a television show watched regularly during pregnancy.