Hearing loss in the child following streptomycin administration during pregnancy.

The risk of deafness developing in the unborn child following the use of streptomycin (SM) during pregnancy remains uncertain. We have followed up 30 children whose mothers received SM during pregnancy. One child (3pc), whose mother received SM during the first trimester of pregnancy, had profound unilateral hearing loss which could possibly be ascribed to SM. This child had however, in addition, features of congenital hypotonia and a unilateral single crease. Two further children had conductive deafness which could not be due to SM, associated with serious otitis media. Although the risk to the foetus of hearing loss following the use of SM during pregnancy appears relatively low it should, where possible, be avoided during the first trimester of pregnancy.

The effect of frequency tolerance on audiometer accuracy.

Investigations into the methods used to calibrate audiometers reveal that the 6 000 Hz frequency is particularly liable to yield inconsistent results when calibrated in the usual way. It is shown that the TDH39 telephone receiver which is usually calibrated on a 9A coupler in accordance with the International Standards Organization recommendation R389 will depend to a considerable extent on the precise frequency used and may differ by as much as 7 db when the frequency is varied but still retained within the specified tolerance limits. A new telephone receiver, the TDH50, is much less sensitive to frequency variation. It is shown that this receiver should be calibrated with the same threshold figures as the TDH39.

Binaural speech discrimination.

The phenomenon of binaural summation in which the addition of signals presented to the two ears simultaneously takes place at a central level, has been known for many years. It is reasonable to assume that the pattern of summation differs between subjects with central lesions and those with lesions in the peripheral auditory tracts. Various tests have been proposed to aid in locating the site of the lesion which compare the monaural and binaural speech discrimination scores. In the present work, two of these tests have been examined. Three groups of subjects have been used: (1) a normally hearing group; (2) a group with hearing impairment resulting from cochlea pathology, and (3) a group with hearing impairment resulting from lesions at the level of the cochlear nuclei. The results showed that neither test differentiated between peripheral and cochlear nuclei lesions.