As you get used to the idea of the baby growing inside you, it’s only natural that you might start talking to her, crooning lullabies and encouraging your partner to chat with your belly. 

It’s not all in vain: Beginning in the second trimester of pregnancy, your baby can detect sounds from outside your body. The voices, tunes and noises she hears in utero do, in fact, help her get used to the environment she’ll enter at birth.

When can babies hear in the womb?

Around week 18 of pregnancy, the structures inside your baby’s ear are well-established enough for your baby to start hearing 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, your baby will hear more and more of the outside world. By weeks 27 to 30, babies react in response to voices and noises that filter into the womb.

When can your baby hear you?

When you’re pregnant, the clearest noise your baby will be able to make out is yours. Most sound is transmitted through the air and then through your uterus. But when you speak, the sound of your voice reverberates through your bones and the rest of your body, amplifying it.

Studies have shown that a fetus’s heart rate increases when she hears her mother’s voice, suggesting your baby becomes more alert when you speak. Reading out loud, carrying on conversations and singing the songs you’ll be repeating to your baby over the coming years will help her to get to know your voice.

Partners shouldn’t despair — babies also learn to recognize other people’s voices (and sounds) that they hear often in utero. Researchers have discovered that newborns react differently to words and sounds that were repeated daily throughout the third trimester compared to those they never heard during pregnancy. So when your partner reads or sings to your baby, she’s learning that voice too!

How hearing develops

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 become 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 the 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.

By week 18 of pregnancy, your baby’s ear is well enough developed to start detecting noises. Around weeks 27 to 30, babies can turn their heads or otherwise respond to sounds they hear outside the womb.

What does it sound like in the womb?

Sounds travel best through open space, which is why you can hear someone yelling more easily in an open field than when your head is underwater in a pool, for instance. And your baby isn’t exposed to open air when she’s still growing inside you: There’s amniotic fluid surrounding her, plus all the layers of your body and the amniotic sac, between her and the world. So even when her ears are fully developed, the sounds she hears in utero are muffled.

Try this for fun: Put your hand over your mouth. Have your partner do the same. Then carry on a conversation. That’s more or less what voices sound like to your baby in the womb. You’ll notice that although you can make out the tones and pitches of a sentence, you might not be able to understand some words.

Similarly, try singing a song with your mouth covered and you’ll hear that the tune comes out loud and clear, but not the lyrics.

The louder a sound, of course, the more likely your baby can hear it. A barking dog, honking horn or wailing siren is going to sound more distinct than quiet background music — but that’s not necessarily a bad thing. The sounds your cutie gets used to in utero will be less likely to startle her after she’s born.

Should you avoid loud noises while pregnant?

In most cases, there’s no reason to avoid a loud situation — whether it’s a concert you’ve been anticipating for months (although you might want to skip the front-row seats) or an especially raucous baby shower. 

The physical barrier of amniotic fluid muffles sounds and makes it harder for baby’s ears to do their job of listening in. Even very loud noises for you won’t sound loud to your baby.

That said, loud noise while pregnant could potentially cause some developmental damage or hearing loss in a growing baby when it’s prolonged and repeated. 

Generally speaking, that means you should avoid eight hours of exposure to continuous noises louder than 85 to 90 decibels (imagine what it sounds like to mow your lawn) or more than two hours a day of noises louder than 100 decibels (like standing near a chainsaw).

If you work on a noisy factory floor for a full shift, for example, it's worth talking to your boss about the possibility of transferring temporarily to a quieter setting.

Should you play classical music for your baby in the womb?

While you might have heard that playing classical music for babies in the womb can boost their IQ or give them a foundation for a better education, there’s no proof that doing so will result in a baby Mozart. (In fact, playing music to your belly all the time could disrupt your baby’s all-important sleep cycles.)

That said, there’s also no harm in putting on your favorite tunes — whether they’re classical sonatas, honky tonk country or rock and roll. Your baby might just learn to love the music and even be soothed by those familiar sound when she’s outside of the womb.

If having a one-sided conversation with your baby feels awkward, remember that starting in your second trimester your baby really is listening to the words you speak. So sing or chat your baby up if you’d like, knowing that she’s soaking in every sound.