my voice

"She is getting used to the sound of your voice - and Dad's too - every time you talk to each other or someone else. That's why infants seem to recognize and respond to their parents' voices at birth. Your voice, because it is heard not only from outside but from inside, is especially familiar, and appears to be comforting, too. Research shows that a fetus's heart rate slows in response to its mother's voice, suggesting that babies are soothed by their moms even before birth."