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Page Five of an eleven-page article:
Noise: A Health Problem
United States Environmental Protection Agency

Noise and the Unborn

"There is ample evidence that environment has a role in shaping the physique, behavior and function of animals, including man, from conception and not merely from birth. The fetus is capable of perceiving sounds and responding to them by motor activity and cardiac rate change."
Lester W. Sontag, The Fels Research Institute

While still in its mother's womb, the developing child is responsive to sounds in the mother's environment. Particularly loud noises have been shown to stimulate the fetus directly, causing changes in heart rate. Related work also has demonstrated that, late in pregnancy, the fetus can respond to noise with bodily movements such as kicking.

Just as the fetus is not completely protected from environmental noise, the fetus is not fully protected from its mother's response to stress, whether it be caused by noise or other factors. When her body reacts to noise, the physical changes she experiences may be transmitted to the fetus. And it is known that the fetus is capable of responding to some changes in the mother's body of the type produced by emotion, noise, or other forms of stress.

In contrast to the more direct risk, this indirect fetal response may threaten fetal development if it occurs early in pregnancy. The most important period is about 14 to 60 days after conception. During this time, important developments in the central nervous system and vital organs are taking place. Unfortunately, women are often unaware that they are pregnant for much of this period, and are thus unlikely to take extra precautions.

While very little research has addressed these questions, due to the difficulties of studying humans in this respect, certain suggestive human research has been done. A Japanese study of over 1,000 births produced evidence of a high proportion of low-weight babies in noisy areas. These birth weights were under 51/2 pounds, the World Health Organization's definition of prematurity. Low birth weights and noise were also associated with lower levels of certain hormones thought to affect fetal growth and to be a good indicator of protein production. The difference between the hormone levels of pregnant mothers in noisy versus quiet areas increased as birth approached.

Studies have also shown that stress causes constriction of the uterine blood vessels which supply nutrients and oxygen to the developing baby. Additional links between noise and birth defects have been noted in a recent preliminary study on people living near a major airport. The abnormalities suggested included harelips, cleft palates, and defects in the spine.

Taken together, this information points to the possibility of serious effects of noise on the growth and development of the unborn child. While it cannot be said at what level maternal exposures to industrial and environmental noise are dangerous to the fetus, these findings do create some concern. It is known that extreme stress of any type will certainly take a toll on the fetus, but, in the case of noise, it is not known how much is required to have an effect. Whatever the effect, the risk of even a slight increase in birth defects is considerably disturbing.

The fetus is not fully protected from noise

Noise may threaten fetal development

Noise has been linked to low birth weights

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This page from the USEPA Report is part of Section Seven:
The Harm section of