What and when can a fetus hear?

By Amanda Barrell     

Reviewed by Valinda Riggins Nwadike

Fetal hearing | Differentiating
voices | Loud noises | Music | What does it sound like in the womb? | Summary


People often wonder if a fetus
can hear while in the womb. Many expectant parents will speak to or play music
for a developing fetus.


Evidence suggests that the
auditory system starts forming at the 18th week of pregnancy and continues to
develop until the baby is between 5 and 6 months of age.
Everything that the fetus
hears will contribute to this process. In this article, we look at what a fetus
can hear at different stages of development.

Fetal hearing at each stage of
development


Despite being close to a
lentil in size, an embryo will begin to develop ears during the 2nd month of
pregnancy. The ears start as tiny folds of skin on the sides of the head. After
the 8th week, the embryo becomes a fetus.
According to Mayo Clinic, the
ears begin to stick out from the head at 18 weeks, and the fetus may become
able to hear. At this stage, the brain starts to designate the areas that will
govern smell, taste, vision, touch, and sound.
By 22 to 24 weeks, the fetus
will be about the size of a mango and will start to hear low-frequency noises
from outside of the womb.
As the fetus grows and their
sense of hearing develops, they will be able to distinguish an increasing
number of different sounds.
Research suggests that the
most vital time for the development of hearing is between 25 weeks of pregnancy
and 5 to 6 months of age.
By the time babies reach the
age of 6 months, they will be able to turn their eyes or head toward the source
of a sound.
Newborns in the United States
usually receive a hearing test before leaving the hospital or within 3 weeks of
birth.

Can they differentiate between
different voices?


At first, a fetus cannot
distinguish between different voices.
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.


Are loud noises bad for the
fetus?


Many people wonder whether it
is safe to attend a loud concert or work in a noisy job while pregnant. While
occasionally hearing loud sounds is unlikely to be harmful, research has found
that prolonged exposure to loud noises may contribute to hearing loss in the
baby.
Examples of noisy jobs include
those that involve people working in close proximity to:

  • loud music
  • crowds
  • sirens
  • trucks
  • airplanes
  • machinery
  • guns
According to the National
Institute for Occupational Safety and Health, researchers are unsure of what
noise levels are safe for a developing fetus.
However, taking into
consideration how sound travels through the body, they recommend that pregnant
women avoid very loud situations — anything louder than 115 decibels, which is
about as loud as a chain saw — as much as possible.

Can the fetus hear music?

The noises that a fetus hears
from around week 23 of pregnancy are vital to their future hearing.
Specific parts of the auditory
system need these noises to develop properly. As such, scientists recommend
exposing a fetus to both speech and music.
Many people believe that
playing classical music to a growing fetus will help brain development and
boost IQ, but there is little evidence to support this claim.

What does it sound like in the
womb?


It is noisy in the womb. As
the fetus’s auditory system develops, it will encounter all types of sound from
within the woman’s body. These include the heartbeat, as well as the noises of
the blood flow and digestive system.
Around the 23rd week of
pregnancy, the fetus will also be able to hear noises from outside of the womb.
These include speech and music. As the fetus develops, all of the sounds will
become louder and more distinguishable.
Amniotic fluid surrounds the
growing baby in the womb, and the woman’s body tissues encase them, so noises
from outside the body will sound muffled.

Summary

The ears of a fetus start to
develop relatively early in pregnancy. However, hearing does not develop until
the auditory system, the brain, and certain pathways start to form, which
usually occurs between weeks 22 and 24.
The auditory system requires
stimulation through speech, music, and other sounds to grow properly. As it
does, the fetus will be able to hear more and more.
A baby’s hearing continues to
develop after birth, until around 5 or 6 months of age.





SOURCE: MEDICAL NEWS TODAY
Kayode Ojo
Kayode Emmanuel Ojo is the Co-Founder and Managing Director at SHEFFA Limited. He is presently studying Computer Science at the National Open University, Victoria Island, Lagos.