Paediatrics: Hearing assessment

Hearing assessment

A foetus will respond to sound in the latter part of pregnancy (from 3rd trimester). At birth, the baby will react to noise with a marked preference for voices.

Hearing screening

Specific screening questions can be asked when evaluating hearing:

•   Birth: does baby startle to loud noise?

·  12wks:

•   Does baby quieten to mother’s voice even when mother cannot be seen?

•   Does baby quieten to prolonged loud noise?

•   Does baby settle to a musical toy?

•   5mths:

•   Does baby smile to familiar voice?

•   Does he/she take turns to vocalize when spoken to?

•   7mths:

•   Does baby turn to look towards a new sound?

•   Does he/she make tuneful vocalization?

•   9mths:

•   Does baby recognize own name?

•   Does baby recognize and react to familiar tunes and music?

•   11mths: Will baby react to calling from out of sight?

The early detection of hearing loss is important. Deafness impairs speech and language development, cognitive development, and socialization. A baby who does not startle when parents come into view may not have heard them approach due to deafness. These children need urgent audio-logical assessment along with children who show absence of appropriate vocalization by age (see bullet points in Hearing screening).

Hearing tests

All health authority areas in the UK have a universal newborn hearing screening (UNHS) programme. UNHS involves otoacoustic emission test-ing in the first 48hr after birth. In the test a small earpiece is inserted into the ear canal. This delivers a sound that evokes an emission from the ear if the cochlea is normal.

Current hearing screening programmes (Table 24.1)

There is currently some regional variation in the type of tests used.

In line with recommendations once UNHS is in place, universal distrac-tion testing at 7–9mths will be abandoned.

The distraction test

The test is based on the principle that a normal response is observed when sound is presented to an infant, and the infant turns their head to lo-cate the source of the sound. Two testers are required—one presents the sound out of the infant’s line of vision, while the other holds the infant’s attention in a forward direction. The test involves delivering a frequency— specific stimulus presented at quiet levels (35dB) to the side and slightly behind an infant who is seated on a parent’s knee.

Distraction testing requires a behavioural response and is therefore a direct test of hearing sensitivity. The major disadvantages of this test are that an infant must be mature enough to sit erect and head turn, and it is subject to all the common biases found in behavioural testing of hearing. It is therefore unsuitable for neonates, which makes identification of hearing loss before 6mths of age very difficult.