"Since babies are in constant motion when they're in the womb, being laid in a stationary crib can be unsettling for them," Klaassen says.

Zalon also notes that complete silence can be unsettling. While in utero, babies were barraged with sounds of Mom's blood rushing, heart pumping, stomach churning and, perhaps, other, less-pleasant noises, as well. "White noise, soft voices or calming lullabies ... can all be soothing to Baby," she says.

Walker recommends using a white-noise machine. "The noise coaxes the brain into that restful state, but only if it is loud enough," she says.

This sounds counterintuitive (aren't we always "shushing" people around babies?) until you remember the high-decibel womb setting your child only recently left. "Re-creating some aspects of the womb environment will soothe babies very well," Walker says. "It was much louder than you think."

Other white-noise sources include your bathroom fan, a radio set to AM/FM stereo static and running water.

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