Can Babies Hear In Utero? Answers From An Expecting Ear Doctor

As an otologist (AKA ear doctor), I’ve  spent the better part of a decade training to understand and treat hearing loss in children and adults. But, it wasn’t until my own recent pregnancy that I began to ponder the specifics of hearing development. I began to wonder...

“Can my baby detect sound in utero?”

“Will she recognize my partner’s and my voice after she is born?”

“Does talking, reading, or playing music for my bump influence her developmental growth?” 

Now, at 7 months pregnant, I find it thrilling to think that she is already starting to eavesdrop on my conversations, even before she has joined our world. And so, in an effort to better understand how hearing develops in utero and answer my own questions, I compiled some relevant literature. For you. For me. For all curious new parents. Read on!

How the ear works

Before we cover what your baby hears, let’s talk about how hearing works in general.

The hearing system consists of three parts: the outer ear, the middle ear, and the inner ear. The outer ear is comprised of the pinna (auricle), the ear canal, and the eardrum (tympanic membrane). 

The middle ear is a small, air-filled space with a chain of three small hearing bones (malleus, incus, and stapes), termed ossicles, that are suspended in space by tiny ligaments, and make small movements in response to sound waves hitting the eardrum. The malleus is attached to the eardrum, linking the outer ear to the middle ear. The stapes connects the middle ear to the inner ear. 

The inner ear has two primary functions: hearing and balance. The hearing portion of the inner ear is handled by the cochlea, which is derived from a Greek word for “snail” because of its distinctive coiled shape. The cochlea contains special fluid that moves in response to small vibrations of the stapes and stimulates hundreds of thousands of sensory cells (“hair cells”) which transmit sound waves into electrical responses that are sent to the brain through the hearing, or auditory, nerve.

Then, the brain decodes the information sent by the auditory nerve into all the different sounds that we hear, as children and adults!

How your baby’s hearing develops in utero

At approximately 5-6 weeks gestational age (GA) – this may be around the time that you discover you’re pregnant – your baby has already begun to develop some of the basic components of the inner ear. 

Throughout your first and second trimesters, your baby’s ears continue to develop.

The cochlea matures, developing different compartments and sensory cells (“hair cells”), and specialized neurons form that transmit sound from the outside world to your baby’s brain. The small hearing bones of the middle ear, which vibrate in response to sound waves, will also develop around this time. But your baby can’t hear anything...yet. 

It’s not until you’re almost half-way through your pregnancy (19 weeks GA) that your little one is able to detect his or her first sounds. 

Most of these noises are from mom’s body (i.e. your heartbeat, breathing, and the gurgling of your stomach) but some low frequency sounds from the external environment can get through even at this early stage. For example, if you’re listening to music, your baby may be listening too, but with the “bass” register turned up and the “treble” register turned down. Studies have shown that auditory responsiveness (i.e. the baby moving or even turning his head in response to noise) begins around 24 weeks GA and continues to progress over the next 13 weeks, with improved responsiveness to a wide range of frequencies as he grows.

In the third trimester, your baby can already recognize mom’s voice, as indicated by an increase in heart rate, suggesting that he or she is more alert. Amazingly, infants seem to show preference for their mom’s voice soon after birth and researchers hypothesize that this finding is due to repeated prenatal exposure of mom’s voice as well as the idea that the maternal voice reverberates through the larynx and diaphragm, perhaps allowing baby to become more sensitized to it while in utero.

How I feel about my baby’s hearing in utero

As a doctor in this field and expecting new mom, I find it exciting to think that my daughter has already begun forming critical auditory pathways between the peripheral inner ear and her brain. That she will grow and develop throughout her life with stimulation from speech, music, and other sounds of the world!

Am I concerned about anything at this point? Many soon-to-be moms and dads are concerned that loud noises will damage their baby’s hearing in utero. While prolonged exposure to noise can cause some developmental damage or hearing loss, don’t despair if you’re exposed to the occasional loud sound (such as a siren blaring or a concert). Typically, these infrequent instances will not affect hearing development. In most cases, it’s best to continue with your normal life and expose your baby to the same sounds that you hear. After all, those sounds are only a primer for what she will be exposed to throughout childhood!

Do I talk to or play music for my bump? Even though some research has shown that babies recognize certain voices or sounds after birth, there is no evidence that speaking to your bump or playing music will significantly impact your baby’s long-term language acquisition or developmental skills. Still, if you want to read stories, sing lullabies, or play some music for your developing baby, there is certainly no harm, especially if you enjoy it! I certainly do.

Sources:

1. Lim R, Brichta AM. Anatomical and physiological development of the human inner ear. Hear Res. 2016. doi:10.1016/j.heares.2016.02.004
2. Hepper PG, Shahidullah BS. Development of fetal hearing. Arch Dis Child. 1994. doi:10.1136/fn.71.2.f81
3. Crade M, Lovett S. Fetal response to sound stimulation: Preliminary report exploring use of sound stimulation in routine obstetrical ultrasound examinations. J Ultrasound Med. 1988. doi:10.7863/jum.1988.7.9.499
4. Hirnholz JC, Benacerraf BR. The development of human fetal hearing. Science (80- ). 1983. doi:10.1126/science.6623091
5. Kisilevsky BS, Hains SMJ, Lee K, et al. Effects of experience on fetal voice recognition. Psychol Sci. 2003. doi:10.1111/1467-9280.02435
6. Spence MJ, DeCasper AJ. Prenatal experience with low-frequency maternal-voice sounds influence neonatal perception of maternal voice samples. Infant Behav Dev. 1987. doi:10.1016/0163-6383(87)90028-2
7. Moon CM, Fifer WP. Evidence of Transnatal Auditory Learning. J Perinatol. 2000. doi:10.1038/sj.jp.7200448