Answer:
A fetus begins responding to sound at between 22 and 24 weeks but can only hear low frequencies, such as a dog barking or a lawn mower.
As the auditory system and the brain continue to develop, this range increases. By late pregnancy, the fetus can hear voices and distinguish between them.
so they can start to hear in the middle of the 2nd trimester but in the 3rd trimester can hear voices and distinguish between them