We've seen parents-to-be in sappy movies putting headphones or speakers up to the pregnant woman's stomach. Sometimes they're trying to make the fetus listen to some grandparent's voice. Sometimes they're trying to make some kind of crazy-smart super baby. But can a fetus stuck behind thick walls of flesh hear any of it? And if it can, would it hear anything more than muted noise?
First of all, parents-to-be need to be careful with that kind of stuff. The wrong kind of sound, especially low frequency vibrations, could turn a kid into a bony, muscled-over, dead-eyed drone. Some wasps determine what their larvae will develop into by drumming their antennae on the egg chambers, and studies show that young rats exposed to similar vibration lose fat and gain bone and muscle. But how about normal, high-pitched conversation? Surely a fetus couldn't hear anything like that.