The First Sounds Babies Recognise: How Hearing Develops Before Birth

IVAN BERBEROV - SEPTEMBER 26, 2025 

📖 Reading time: 5 minutes and 5 seconds 

The womb is not a silent place. Babies grow to the rhythm of a heartbeat, the rush of blood flow, and the gentle murmur of voices softened by fluid and tissue. From the mid-second trimester, the auditory system begins to develop, with NHS guidance noting that babies may start hearing around week 15 and that hearing continues to mature through week 18 as responses become more consistent.


Classic experiments have shown that newborns, within hours of birth, prefer to hear their mother’s voice over another female voice, which is consistent with the idea that learning and memory are formed before birth. Inside the uterus, lower frequencies travel more easily, so a mother’s voice reaches the fetus both through the air and the body, helping to make it the most familiar sound of all.

When Does Hearing Switch On in the Womb

Think of hearing as a dimmer light switch, not an on–off button. The tiny parts of the inner ear form during the second trimester, then the brain keeps tuning up hearing through the rest of pregnancy. Babies may start to hear from about week 15, and by roughly week 21, they can pick up noises and voices from outside the womb, although everything reaches them softer and lower in pitch because it travels through fluid and tissue. As mothers move toward the third trimester, reactions to sound become steadier and easier to notice.

Public health advice lines up with that picture. NIOSH notes that ears are developed by about week 20 and that many fetuses begin responding to sounds at around week 24. That is why some parents notice gentle startles or settling movements to everyday sounds in the late second and third trimesters. 

 

Researchers also see that the response grows stronger with age. Near term, fetuses change heart rate and activity when they hear their mother speaking, which shows the system is not only receiving sound but also beginning to tell familiar from unfamiliar patterns.

 

Frequency also matters. Earlier work found that by about week 27, most fetuses respond to lower frequency tones, while higher frequencies are less effective until later, which fits with the way the womb filters sound. As a result, parents may see the strongest movements or heart-rate shifts to lower-pitched sounds in the late second trimester, with broader responsiveness developing in the third.

What Sounds Actually Reach the Baby

Inside the womb, the soundscape is closer to being underwater than sitting in a quiet room. Fluid and tissue soften and reshape what gets through. Low notes and rhythms travel well. Higher-pitched details are reduced before they reach tiny ears. Classic measurements describe the uterus acting like a low-pass filter, with high frequencies damped and bass passing more easily. 


The maternal voice has a head start. It reaches the fetus both through the air and through the body’s tissues, so the overall contour of mum’s speech and song carries particularly well. Older clinical summaries note that outside voices are reduced on the way in, yet the mother’s intonation and rhythm remain clear enough to be recognised after birth. That is why the patterns of rhythm and sound matter more than crisp consonants in the womb.

 

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In everyday terms, here is what typically gets through.

  • Heartbeat, blood flow and digestive sounds set a constant low background. These sit mainly below a few hundred hertz, which the womb transmits well.
  • The mother’s speech pattern, melody and timing are audible, even if the sharp edges of consonants are softened. Babies hear the tune of language more than the exact letters.
  • External voices, traffic and household sounds arrive quieter and bass-tilted. Low-frequency parts pass with little loss, while higher frequencies are heavily reduced before they reach the uterus. 

The baby is most likely to pick up soothing rhythms, vowels and the rise and fall of familiar voices. Very high notes and crisp consonant details are less important inside the womb, since the path to the fetus trims those away.

The First Sounds Babies Recognise

The Maternal Voice

One of the most famous newborn studies showed that babies will hear their mother’s voice within hours of birth. Researchers gave infants a special dummy that played either mum’s voice or another woman’s voice, depending on how the baby sucked. 


The babies quickly learned the pattern and chose the setting that brought back their mother’s speech more often, which points to memory formed in late pregnancy. This classic experiment is a clear, friendly way to picture what recognition looks like so early in life.

 

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Rhythm, Melody and Language Cues

Before birth, babies are bathed in the rhythm and melody of speech. That is why newborns already show traces of the language they heard in the womb. In a two-country study, infants only hours old responded differently to native-language vowels compared with foreign vowels, which points to prenatal learning of speech patterns. Reviews and follow-up work support the idea that broad prosody and vowel shapes matter first, with fine consonant detail coming later.


What this looks like in practice:

  • Vowels and rhythm lead the way. Newborns exposed to a language before birth react more readily to its vowel patterns and intonation than to unfamiliar ones. This fits with the physics of the womb, where lower-frequency vowel energy gets through more easily than high-frequency consonant details.
  • Crying reflects the home language. Studies comparing French and German newborns found that cry melodies already mirror the rise-and-fall patterns of the surrounding language, suggesting that rhythm and pitch contours were learned late in pregnancy.
  • Familiar tunes leave a trace. When a melody is played often during pregnancy, babies show stronger brain responses to that same tune at birth and even months later, evidence that repeated prenatal sound can form lasting memory traces.

Babies tune in to the sound of speech first. They are picking up the flow of vowels, the rise and fall of phrases, and the timing of familiar voices. As hearing matures after birth, finer details like crisp consonants become easier to detect, but the early bond to the rhythm and melody they heard in the womb is already in place.

Familiar Tunes and Everyday Sounds

Repeated exposure makes a difference for music, too. In one study, a melody played often during pregnancy triggered stronger brain responses in babies after birth and even months later, suggesting that simple tunes can leave a lasting trace. 


At the same time, findings on whether babies can reliably tell specific outside voices apart in utero are mixed, with some work showing discrimination in late pregnancy and other studies finding limited or no clear voice preferences beyond the maternal voice right after birth. 


Repetition helps, melody is memorable, and the mother’s voice remains the most familiar sound of all.

How Loud Is The Womb

Think of the womb as a gentle, underwater soundscape. Layers of muscle, skin, placenta and fluid soften and reshape what gets through. In practice, that acts like a low-pass filter. Classic measurements in animals and humans show that energy above roughly 500 Hz is cut back substantially by the time it reaches the fetus, whereas the low end carries through much more easily.


The maternal voice has a clear pathway in. It reaches the fetus through the air and also through the body’s tissues, so the overall contour of mum’s speech and song is transmitted effectively inside the uterus, while outside voices are more attenuated. Studies of intrauterine transmission and newborn listening preferences support this picture, with work showing that the maternal voice remains intelligible in a filtered form and is often preferred straight after birth.


Here is what that means in everyday terms.

  • The fetus hears a softened, low-pitched version of the world. Bass and lower mids pass through best. Treble detail is trimmed away by the tissues and fluid.
  • Heartbeat, blood flow and digestive sounds provide a constant low background, which sits mostly in the frequency range that transmits well.
  • Mum’s voice stands out because it travels both through the air and the body, so rhythm and vowel shape reach the fetus more clearly than other people’s speech.

Public health guidance mirrors this idea and adds a practical caution. Very loud environments can still matter because sound can travel through the pregnant body. Agencies note that fetal ears develop by about week 20 and responses begin around week 24, so it is sensible to avoid prolonged exposure to very high levels, even though everyday conversation and typical home noise arrive softened in the womb

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Safe Sound Exposure During Pregnancy

Public health agencies advise reducing long stretches in very loud environments and taking breaks when noise is intense. NIOSH notes that a fetus’s ears develop by about week 20 and responses to sound begin around week 24, and that very loud sounds can pose a risk because sound travels through the pregnant body. 


As a practical yardstick, the NIOSH recommended exposure limit for adults is 85 dBA averaged over an eight-hour day, with advice to avoid impulse peaks around 140 dB. While that limit serves as an occupational guideline, it helps frame why moderation and rest from high noise are sensible during pregnancy.


Clinical reviews suggest extra caution with sustained low-frequency noise. Low frequencies carry well through tissue and can dominate the in-utero soundscape. Reviews and recent studies recommend limiting prolonged exposure to strong, low-frequency levels and following standard safety principles, such as stepping away from loud sources and using hearing protection when in noisy settings.
 

Simple habits that are safe and helpful:

  • Normal conversation, reading and singing are safe ways to bond. The baby will mainly hear rhythm and vowels, so a relaxed voice at everyday volumes is ideal. Public health guidance supports talking and singing regularly during quiet moments.
  • Avoid placing headphones or speakers directly on the bump. NHS guidance in the UK and allied resources advise against this because levels at the uterus can be too high even when the external volume seems modest. Keep music in the room instead, at comfortable levels for you.
  • If you work or spend time in loud places, take regular quiet breaks, increase distance from loud sources, and follow general hearing protection advice. Seek tailored guidance from your midwife or clinician if you have concerns about repeated high-noise exposure.

For a calmer nursery or bedroom, choose the quietest room, then block the main sound paths. Start with windows, since these are often the weakest link: upgrade to acoustic laminated glazing or add secondary glazing with a generous air gap to lift sound insulation without major structural work. 

 

Fit a solid-core door with perimeter seals and a drop seal, and close small leakage paths by sealing gaps around frames, skirtings and sockets with acoustic sealant. If you are renovating, a lightweight soundproofing solution such as MUTE SYSTEM™ 23, can raise wall sound insulation while keeping thickness modest. 

World, Already Familiar

Babies do not arrive in silence. By mid-pregnancy, the hearing system is switching on, and by the third trimester, many fetuses are reliably responding to sound. What reaches them is a softened, low-rich mix where the mother’s voice carries especially well, which helps explain why newborns prefer it within hours of birth.


Everyday conversation, reading and gentle music at comfortable levels are safe ways to bond, while long stretches in very loud places are best avoided. If you want a simple rule, choose calm, regular moments to talk or sing and steer clear of pressing headphones to the bump. These habits fit public health guidance and the science of how sound travels to the womb.


If you are curious about creating quieter spaces at home, in clinics or in community settings, that is our craft. We design environments that support healthy acoustics by managing noise at its source and shaping peaceful soundscapes for families.

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