Will playing classic music through headphones attached to your pregnant belly make your baby smarter? Probably not, but your baby certainly can hear what's happening in the outside world.
Your baby's ears start to form around week eight of pregnancy and, by week 24, they are structurally complete. Research shows that babies can hear sounds outside of the womb beginning late in the second trimester.
Don't wake the baby!
Many experts agree that your baby can actually be startled by loud, unexpected noises in the third trimester. These noises can cause a change in heart rate or jerky movements. The American Academy of Pediatrics says the whooshing sound your baby hears inside the womb sounds louder than a vacuum cleaner to him or her.
The sound of your voice
The sounds that your baby hears in utero are muffled but recognizable. Some studies have shown that a fetus calms down (heart rate slow) when hearing the sound of the mother's voice. So you are already comforting your little one before he or she's even born.
The effects of music
It's the tone and inflection of your voice that the baby recognizes, not your exact voice. And, as with talking, your baby can also recognize music. However, some people believe that music played to your baby in the womb will actually make him smarter. The Mozart effect claims that listening to classical music will improve your baby's neural connections and brain development in utero. That's why you hear about so many pregnant women pumping classical music through headphones into their belly. No actual scientific evidence supports this theory. So, if you'd rather listen to Bob Marley than Bach, that's alright. In fact, the outside world provides enough fetal acoustic stimulation that you don't need to do anything extra.