When you are pregnant, exposure to loud noises can raise the risk of hearing problems and other health issues not only for you, but also for your unborn baby. Loud noises can come from a variety of sources, including airplane engines, rock concerts, workplace-associated noise or a car radio played at a high volume. Avoiding loud noises doesn't necessarily mean sticking to a completely silent environment, however, since soft sounds actually might be beneficial to your unborn child.
What Babies Hear in the Womb
Your unborn baby's outer, inner and middle ear are well-developed by 24 weeks gestation. The cochlea has formed by this point, so the baby's ear can effectively transmit sounds to the brain for processing. Sometime between 27 and 30 weeks gestation, the fetus begins to respond to sounds from outside the womb.
Sounds Are Muffled
In most cases, even sounds that seem loud to you might be muffled in the womb. The walls of the uterus, and fat and muscle in the abdominal cavity all dampen sound waves and lower their volume before they reach your baby's ears. The amniotic fluid fills the inner ear, preventing the eardrum from amplifying sounds in the way it will once your baby is born and also dampens high-pitched noises; however, amniotic fluid actually amplifies low-pitched sounds slightly.
The Effect of Loud Noises on the Fetus
Continuous exposure to sounds over about 90 to 100 decibels, about the level of a chainsaw, can raise your unborn baby's risk of hearing loss, according to What to Expect. It also can increase the chances of giving birth prematurely and of having a low-birth weight baby. Shorter occasional exposure to sounds in the 150 to 155 decibel range, the level next to a jet engine, can lead to similar problems. A sudden loud noise also can startle an unborn baby, causing increased activity shortly after the fetus hears the sound.
Soft Music Soothes Mom and Baby
While excessively loud sounds potentially can cause harm to your baby, softer sounds might provide some benefit. Exposure to pleasant music played at a level of 70 decibels or lower can soothe both mother and baby. Avoid discordant music at any volume, since animal studies have indicated changes in brain structure when fetuses are exposed to this kind of music, according to Baby Center. Because the impact of music on unborn human babies has not been well-studied, the full impact of sound on fetuses remains unknown.