THE FETUS AND NOISE

From 23 weeks of gestation some and from 28 weeks all healthy fetuses are capable of reacting to sound stimulation. The intrauterine acousti c environment is dominated by maternal sounds - heartbeat, breathing, the mother's voice, borborygmi and sounds caused by body movements. Ba ckground noise is never below 25 dB and can rise to 84 dB when the mot her is singing. Noises that are meant to reach the fetus must be loude r than the background noise and must be of low frequency as high frequ ency sounds are damped by maternal tissue. Vibroacoustic stimulation t ests (VAST) have become popular in pregnancy surveillance over the las t 20 years, mostly using an artificial larynx. Advantages and problems of the various VAST protocols in fetal monitoring are discussed in th e light of animal experiments and clinical studies. Health legislation laws in most countries forbid pregnant women to work in surroundings with a high noise level (80dB continuous noise and/or rapid impulse no ise changes of 40dB). Whereas regulations for pregnant women are easy to enforce in industry, pregnant women employed in discos or performin g as musicians spend most of their working day exposed to noise impact higher than the recommended limit.