A baby could hear your voice and other sounds from about 23 weeks of pregnancy.
Around week 6 of pregnancy, even though your little embryo is still smaller than a pea, the cells inside her developing head are already beginning to arrange themselves into unique tissues that will eventually be her brain, face, eyes, ears, and nose. By week 9, small indents will appear on the sides of your baby's neck — although they're not in their final location yet, they will gradually move up and become tiny, curled up, cute-as-a-button ears that you'll gawk over when your baby is born.
Throughout your first and second trimester, your baby's ears continue to develop: The inner ear connects with neurons in the brain responsible for processing sounds, and the miniscule bones of the middle ear (which sense the vibration of sound waves) form. Around week 16 of pregnancy, it's likely that these structures are well-established enough for your baby to start detecting some limited noises.
Some of these are sounds that you might not even notice yourself — the gurgle of your stomach and whoosh of air in and out of your lungs. Over the next few weeks though, your baby will hear more and more of the outside world. By week 24, babies have been shown to turn their heads in response to voices and noises.