Fetuses, Infants May Be Hurt by Loud Noise, Researcher Says

Loud noises like those encountered in some factories, at rock concerts or near airplanes may possibly harm hearing and brain development in fetuses and newborn infants, a University of Washington otolaryngologist reported here Monday.

Experiments in animals show that fetuses in the third trimester of pregnancy and newborns during their first year are considerably more sensitive to noise than are adults, Edwin W. Rubel said. Fetuses at an earlier stage of pregnancy are not susceptible to damage, he said, because the ear is not fully formed.

Fetuses are much more sensitive to low-frequency sounds than are adults, he said. After birth, the spectrum of sensitivity gradually becomes more balanced, encompassing more middle- and higher-frequency sounds.

Rubel performed two types of experiments in chickens. In the first set, he exposed chicken embryos near the end of their maturation or chicks up to 6 weeks old to sound intensities similar to those of a jet engine for four hours or longer. He found that the sound caused the death of a significant fraction of the sensory cells in the chick’s inner ears.

Having shown that sound would damage the sensory cells, he then performed a second set of experiments in which the cells were damaged by surgery or by drugs. In these experiments, he found that damage to the sensory cells caused damage to brain cells that receive electrical signals from the sensory cells.

He observed that as many as 30% of these brain cells died and that the remaining cells shrunk by as much as 20%.

Rubel was very conservative in extrapolating these results to humans, however.

“Nobody really knows for sure how much the fetus hears,” he said. “We know that it hears something, but it is in a completely different type of environment.