When Can Your Baby Hear You in the Womb?

What does the evidence say about when baby can hear sounds in the womb during pregnancy?

1. CDC states that fetal ears develop by about 20 weeks and fetuses begin responding to sounds around 24 weeks. It advises avoiding routine noise above 115 dBA and explains that maternal hearing protection does not fully protect the fetus. 1
2. An ultrasound-observed behavioral study tested pure tones from 19 to 35 weeks. The earliest response occurred at 19 weeks to 500 Hz; responses to higher frequencies appeared later, with all tested fetuses responding to 1,000 Hz by 33 weeks and 3,000 Hz by 35 weeks. 2
3. In a small randomized-order experiment of 25 newborns less than two hours old, behavioral responses were more frequent to the maternal voice than to unfamiliar female voices. This suggests prenatal familiarity but measures newborn behavior, not fetal comprehension. 3
4. A pilot study exposed fetuses to a maternal nursery rhyme twice daily from 34 weeks, then measured 34 infants. Newborn brain responses differed for maternal versus unfamiliar speech, but familiarity with the repeated rhyme did not produce the expected effect. 4
5. A systematic review of 46 third-trimester fetal brain-imaging studies found auditory activation and some evidence of stronger or faster responses with gestational age. Methods varied enough that the review could not establish a single precise maturation timetable. 5

Is when baby can hear sounds in the womb safe in each trimester?

• First trimester. The auditory system is developing, but fetal responses to external sound are not expected this early. There is no evidence-based reason to play recordings to the abdomen in the first trimester.
• Second trimester. Behavioral studies first detect responses to low-frequency sound around 19 weeks, while CDC summarizes fetal response beginning around 24 weeks. A movement response is not the same as mature hearing or understanding.
• Third trimester. Responses extend to higher frequencies and become more consistent as the auditory system matures. The fetus still hears a filtered sound environment, and louder is not better.