The reliability of the Neonatal Oral-Motor Assessment Scale

Sucking problems in preterm infants can be specified by means of visual observation. The Neonatal Oral-Motor Assessment Scale (NOMAS) is the visual observation method most commonly used to assess the non-nutritive sucking (NNS) and nutritive sucking (NS) skills of infants up to approximately 8 weeks postterm. During the first 2 min of a regular feeding the infant's sucking skill is assessed, either immediately or on video. Although NOMAS has been used since 1993, little is known about the method's reliability. The aim of our study was to determine the test-retest and inter-rater reliability of NOMAS.

The 75 infants included in this study were born at 26-36 weeks postmenstrual age (PMA). Four observers participated in the study. They were trained and certified to administer NOMAS in the Netherlands by M.M. Palmer between 2000 and 2002.

We found the test-retest agreement of NOMAS to be 'fair' to 'almost perfect' (Cohen's kappa [kappa] between 0.33 and 0.94), whereas the inter-rater agreement with respect to the diagnosis was 'moderate' to 'substantial' (Cohen's kappa, between 0.40 and 0.65). As a diagnostic tool, however, the current version of NOMAS cannot be used for both full-term and preterm infants. For a measuring instrument such as NOMAS, one should aim at reliability coefficients for inter-rater and test-retest agreement of at least 0.8. A Cohen's kappa of 0.6 or less we find unacceptable. Nonetheless, by observing sucking and swallowing according to a protocol much useful information can be gathered about the development of an infant's sucking skills. For instance, whether the infant is able to co-ordinate sucking and swallowing, whether the infant can maintain sucking, swallowing and breathing during the continuous phase and whether the infant is able to suck rhythmically with equally long bursts. In addition, NOMAS offers useful aids for intervention.

NOMAS should be re-adjusted in order to improve inter-rater agreement, and at the same time current insights into the development of sucking and swallowing should be incorporated in the method.