HUMAN FETAL AUDITORY THRESHOLD IMPROVEMENT DURING MATERNAL OXYGEN RESPIRATION

It has been suggested that the near full-term fetus in-utero has a sen sori-neural hearing loss compared to the neonate due to the relative h ypoxia resulting from placental oxygenation compared to pulmonary oxyg enation. This hypothesis was tested by estimating the threshold of the fetus to vibro-acoustic stimulation applied to the maternal abdomen w hile the mother was breathing room air and again when breathing oxygen . Fetal response was assessed by maternal perception of fetal movement and by objective demonstration of movement by ultrasound. It has been shown that the fetal responses are to the acoustic component of the s timulus, that the acoustic stimulus is not overly attenuated or masked , and that maternal oxygen inhalation enhances fetal oxygenation. The results showed that the threshold was lower and/or the response was st ronger when the mother was breathing oxygen compared to when she was b reathing room air. Thus it is confirmed that in-utero the fetus has an hypoxia-induced sensori-neural hearing loss. At birth, with the shift to more efficient pulmonary oxygenation, there is an improvement in a uditory threshold.