Neonatal Oral Motor

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Psychometriccharacteristics of theNeonatal OralMotorAssessment Scale inhealthy preterm infants

Tsu-Hsin Howe PhD, Department of Occupational Therapy,Steinhardt School of Culture, Education, and HumanDevelopment, New York University, NY, USA.Ching-Fan Sheu PhD, Institute of Cognitive Science,National Cheng-Kung University;Yu-Wei Hsieh MS;Ching-Lin Hsieh* PhD, School of Occupational Therapy,College of Medicine, National Taiwan University, Taiwan.

*Correspondence to last author at School of OccupationalTherapy, College of Medicine, National Taiwan University,17, Floor 4, Xuzhou Road, Zhongzheng District, Taipei 100,Taiwan.E-mail: [email protected]

We examined the reliability, validity, and responsiveness of theNeonatal OralMotor Assessment Scale (NOMAS) in healthypreterm infants. Feeding records of 147 infants (71 males, 76females; gestational age [GA] 36wks), taken from the daybottle-feeding was initiated to the day the infants weredischarged, were used to examine the psychometric propertiesof the normal and disorganized categories of the NOMAS. Theinfants, with or without experience of breastfeeding, were allfed by bottle, with either formula and/or breast milk. GAranged from 24 to 35.9 weeks (mean 29.7wks, SD 2.7) andbirthweight ranged from 470g to 2570g (mean 1251.1g, SD425.9). Postmenstrual age (PMA) at the starting point of bottle-feeding ranged from 29.4 to 40.1 weeks (mean 33.8wks,SD 1.7). We found that the NOMAS had satisfactory internalconsistency (Cronbachs >0.70) in the normal category for 32to 35 weeks PMA. Moderate correlations were found betweenscores on the NOMAS and feeding performance for all age

groups except for PMA of

36 weeks (absolute Spearmansr

s =0.51 0.69), indicating acceptable convergent validity. TheNOMAS demonstrated moderate responsiveness to changes inoralmotor skills in every 2-week period, ranging from 32 to 36weeks PMA (standard response mean greater than 0.5). Thisstudy demonstrated that the normal and disorganizedcategories of the NOMAS are useful, with acceptablepsychometric properties, in assessing oralmotor function inpreterm infants aged 32 to 35 weeks PMA. Future research oninfants with abnormal oralmotor skills is needed to furthervalidate psychometric properties of the dysfunction category of the NOMAS.

Nutritive sucking is considered the most complex activity of infancy. 1 Compromised sucking skills can result in suboptimalnutrition and growth. Research findings suggest that suckingcan be a sensitive indicator of central nervous system integri-ty, differentiating stressed from non-stressed infants, where-as standard neurological examinations may fail to do so. 24

Recognition of normal and deficient sucking patterns is espe-cially important in preterm infants, because feeding prob-lems are one of the prominent developmental issues in thatpopulation. 5 A scientifically sound feeding assessment is thusneeded both for clinicians and researchers to detect feedingproblems and to monitor the success of intervention.

An assessment tool should be scientifically sound in threebasic psychometric properties: reliability, validity, and respon-siveness. 6 Reliability addresses the degree to which an assess-ment tool is free from random error. 7 Approaches for exam-ining reliability include internal consistency reliability, typi-cally examined using Cronbachs coefficient , and testretestor interobserver reliability. Validity indicates whether thetool measures what it purports to. 8 It can be established by demonstrating a high correlation between the tool and acriterion standard (i.e. concurrent validity). In the absence

of a criterion standard, validity is established by assessingthe degree to which the assessment tool correlates withothers measuring related entities (convergent validity). 6

Responsiveness assesses the ability of a tool to detect changeover time. 9 A responsive measure is essential for documentingclinical changes and for outcome studies.

The Neonatal OralMotor Assessment Scale (NOMAS) isa clinical tool commonly used to evaluate the oralmotor skills of neonates who demonstrate reflexive sucking. Severalstudies have reported the results of reliability and validity of the NOMAS. 1014 However, limitations were found in thesestudies. First, examinations of internal consistency and respon-siveness of the NOMAS were not performed in any of thesestudies. Second, the sample sizes in these studies, ranging from11 to 40, were small, which limited the scope of generaliza-tion from these results. Third, the age of the samples studied,ranging from 34 to 49 weeks postmenstrual age (PMA), may not adequately represent the characteristics of younger preterminfants. Thus, the evidence supporting the psychometric prop-erties of the NOMAS remains inconclusive.

The purpose of this study was to examine the psychomet-ric characteristics of the NOMAS. These included the reliabil-ity (internal consistency), validity (convergent validity), andresponsiveness of the NOMAS in healthy preterm infants.

MethodDATA

The data were originally collected for a longitudinal study toexamine the factors related to bottle-feeding in preterminfants. 15 It was conducted at the Mount Sinai Medical Center in New York City with the approval of the institutional review board of the hospital. All medical charts in the NeonatalIntensive Care Unit from July 2001 to July 2003 were reviewedusing a standardized form. Infants who met all of the followingcriteria were included: (1) born at a gestational age (GA) of nomore than 36 weeks; (2) free from any major neurological, car-diac, gastrointestinal, or congenital impairment; with neuro-logical impairment, including but not limited to, documentedabnormal neurological findings, i.e. grade III or IV intraven-tricular hemorrhage or periventricular leukomalacia, cardiac

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impairment, including but not limited to, atrial and ventricu-lar septal defects, gastrointestinal impairment, including butnot limited, to necrotizing enterocolitis, and congenitalimpairment including but not limited to orofacial anomaliesand Down syndrome; (3) having had at least one feedingassessment during hospital stay with record of the NOMAS;(4) fed by bottle with or without breastfeeding experience;and (5) fed either formula milk or breast milk. Records for atotal of 147 preterm infants were included in this study.

PROCEDURES

Records of the NOMAS and feeding performance were col-lected from chart review. As per hospital protocol, bottle-feed-ing was initiated when an infant was medically stable and

when feeding delivery method had progressed from contin-uous feeding (the default method for infants weighing lessthan 1250g in this unit) to bolus feeding. The infant was thenreferred to the occupational therapy service for a routinefeeding assessment and intervention. Observed bottle-feed-ing was recorded by the occupational therapist after eachfeeding session as part of a routine progress report.

A general protocol was followed for each feeding session.

The infant was gently aroused to an awakened state, in whichthe eyes were open and motor activity was present. Sucking was evaluated with the infant in a semi-reclined position withthe neck and head held in neutral alignment. Non-nutritivesucking was rated by observing the infant sucking on thepacifier for 30 seconds. Nutritive sucking was then rated by having the infant suck on an artificial nipple while ingestingthe formula specified in the infants medical orders. The

infants oralmotor responses were observed for a 5-minuteperiod during feeding with removal and re-entry of the nip-ple two or three times. The infants behaviors were recordedon the NOMAS. Bottle-feeding then continued until theinfant finished the required amount or the infant stoppedsucking for over 2 minutes. The amounts of milk and timetaken were recorded.

The infants feeding performances were routinely assessedand documented by an occupational therapist twice or thriceper week. The administrations of the NOMAS for all infants

were performed by an occupational therapist (the first author of this paper), who has been certified by Ms M Palmer, thedeveloper of the NOMAS, to perform the assessment. Therecords of the NOMAS and feeding performance wereextracted from occupational therapy progress reports fromthe day of initiation of bottle-feeding to the day of dischargefrom the hospital. Records obtained were divided into fivegroups according to the infants PMA. These were 32, 33, 34,35, and at least 36 weeks.

MEASURES

The version of the NOMAS used in the study, revised by

Palmer et al. in 1993,12

is a 27-item checklist of feeding char-acteristics observed during nutritive sucking. On the NOMAS,infants are scored for their overall classification of normal,disorganized, or dysfunctional patterns. Disorganized feed-ing is characterized by arrhythmic jaw movements, difficulty coordinating sucking, swallowing, and breathing, and aninability to slow down the sucking rate for nutritive intake.Dysfunctional feeding is an atypical pattern characterized by abnormal jaw excursions or flaccid tongue. However, thedysfunction category of the NOMAS could not be examinedbecause most of the infants included in this study did notshow atypical feeding patterns.

Because there was no scoring system proposed by theoriginal author of the NOMAS, 12 items listed in the NOMAS

were coded as 0 or 1 point to represent absence or presenceof the observed behavior respectively. The total possiblescore for the normal category is between 0 and 9, and that for the disorganized category is between 0 and 13.

Infants feeding performance was measured by transition-al rate. The transitional rate was calculated by the ratio of feeding intake (in milliliters) to the feeding duration (in min-utes). The volume of milk was the amount of milk that infantconsumed by bottle at one observed feeding. The time wasmeasured as soon as the bottle was introduced and suckinghad begun. Any interruptions such as burping and allowance

916 Developmental Medicine & Child Neurology 2007, 49: 915919

Table I: Characteristics of preterm infants ( n =147)

Characteristic

Sex (Male/Female) 71/76Gestational age (wks)

Mean (SD) 29.7 (2.7)Range 2435.9

Birthweight (g)Mean (SD) 1251.2 (425.9)Range 4702570

PMA first oral feed (wks)Mean (SD) 33.8 (1.7)Range 29.440.1

PMA, postmenstrual age.

Table II: Estimated values (95% confidence intervals [CI]) of Cronbachs coefficient for normal and disorganized categories of Neonatal OralMotor Assessment Scale

Postmenstrual age n Normal Disorganized (wks) Cronbachs 95% CI Number of items a Cronbachs 95% CI Number of items a

32 37 0.83 (0.74 0.92) 9 0.72 (0.59 0.86) 1133 74 0.82 (0.76 0.89) 9 0.65 (0.54 0.77) 1234 95 0.82 (0.76 0.88) 9 0.63 (0.52 0.74) 1135 79 0.70 (0.60 0.81) 8 0.68 (0.57 0.78) 11 36 56 0.64 (0.49 0.79) 5 0.64 (0.50 0.79) 7

aTotal number of items for normal category is nine; that for disorganized category is 13. Actual numbers of items used for analysis varied by postmenstrual age because of lack of response variability.


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for breathing during feeding were included as part of thefeeding. The time was recorded when infant finished his/her required amount or stopped sucking for over 2 minutes.

STATISTICAL ANALYSIS

ReliabilityThe internal consistency of both the normal and disorga-nized categories of the NOMAS was examined at 5 PMA groups using Cronbachs . An coefficient greater than0.70 was considered a minimal reliability criterion. 16

ValidityThe convergent validity of the NOMAS was assessed by exam-ining the relations between total scores of the NOMAS in bothcategories and infants feeding performance using Spearmansrank correlation. Correlations between 0 and 0.25 indicatelow validity of the measures; those between 0.25 and 0.5indicate fair validity; those between 0.5 and 0.75 indicatemoderate to good validity; and those greater than 0.75 indi-cate good to excellent validity. 17

Responsiveness

Responsiveness was examined to determine whether theNOMAS can detect changes in oralmotor skills over time(from 3236wks or older) using standardized response means(SRMs). SRMs were calculated by the mean change scoresdivided by the SD of the change scores. An effect size greater than 0.8 was considered large; 0.5 to 0.8 was moderate; and

0.2 to 0.5 was small. 18 In addition, Wilcoxons matched-pairssigned ranks tests were performed to determine the statisticalsignificance of the change scores.

ResultsThe sample cohort consisted of 147 infants (71 males, 76females). GA ranged from 24 to 35.9 weeks (mean 29.7wks,SD 2.7) and birthweight ranged from 470 to 2570g (mean1251.1g, SD 425.9). PMA at the starting point of bottle-feed-ing ranged from 29.4 to 40.1 weeks (mean 33.8wks, SD 1.7).The baseline characteristics of these 147 infants are shown inTable I.

The number of recorded feedings varied and ranged from1 to 12, with a median of 5. Two infants were recorded only once. Individual feeding records were excluded if values of major variables were missing, i.e. the NOMAS scores, drink-ing volume, and time. Five feeding records were removedfrom the data set before the analysis. In addition, the datarecorded under the dysfunction category were less than 2%of total data. Thus, the data recorded under the dysfunctioncategory were excluded in the analysis.

RELIABILITY Using the criterion of greater than 0.70, internal consisten-cies of the NOMAS for 32 to 35 weeks PMA of the normal cat-egory were deemed acceptable; and the same is true for 32

weeks PMA in the disorganized category (Table II). However,the values of coefficient for PMA of at least 36 weeks in both

Psychometric Characteristics of the NOMAS Tsu-Hsin Howe et al. 917

Table IV: Standard response means (SRM) of normal and disorganized categories of the NeonatalOralMotor Assessment Scale

Postmenstrual age (wks) Normal Disorganized n SRM p a SRM p a

32 to 33 29 0.60


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the normal and disorganized categories and that of 33 to 35 weeks PMA in the disorganized category did not reach thepreset criteria, even though estimates of the 95% CI of thecoefficient covered this criterion value.

VALID ITY

Moderate convergent validity was observed for the NOMASof both the normal and disorganized categories (Spearmansr s=0.51 to 0.69 for the normal category, and r s=0.60 to

0.67 for the disorganized category) for 32 to 35 weeks PMA (Table III). For PMA of 36 weeks or older, the associationbetween the total scores of the NOMAS and feeding perfor-mance was weak (Spearmans r s=0.23 for normal category,and r s=0.26 for disorganized category).

RESPONSIVENESS

The responsiveness of the normal and disorganized categoriesof the NOMAS is listed in Table IV. The normal (SRM=0.411.08,

p


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between the normal and disorganized categories were sym-metrical despite the directions of changes. Items describingsame behaviors were listed in both the normal and disorga-nized categories with opposite directions. For example, con-sistent degree of jaw depression was listed in the normalcategory versus inconsistent degree of jaw depression in thedisorganized category, and rhythmical excursions was listedin the normal category versus arrhythmical jaw movementsin the disorganized category. Therefore, the symmetrical pat-terns were expected because of the symmetrical construct of items in the normal and disorganized categories.

Psychometric properties of the dysfunction category werenot examined because of insufficient data. The dysfunctioncategory of the NOMAS was designed to differentiate infants

with neurological problems. 27 The insufficient data obtainedunder the dysfunction category were expected, becauseinfants with documented abnormal neurological findings,

who may exhibit abnormal jaw and tongue movements (i.e.listed in the dysfunction category), were not included in thedata collection. In addition, PMA was used as a grouping cri-terion, and only a few infants with GA greater than 34 weeks(2/147 infants) had been observed in this study. Therefore,

caution should be exercised when interpreting the results of our findings for infants with GA greater than 34 weeks.

ConclusionIn summary, the normal and disorganized categories of NOMAS demonstrated acceptable levels of convergent valid-ity and responsiveness in a cohort of preterm infants from 32to 35 weeks PMA. However, the NOMAS had modest internalconsistency and poor convergent validity with transitionalrate for preterm infants of PMA of at least 36 weeks in boththe normal and disorganized categories. Further validationresearch is needed to investigate the internal consistency of later PMA and to include infants with abnormal oralmotor skills in order to examine items in the dysfunction category.

Accepted for publication 31st July 2007.

Acknowledgments We express our appreciation to Dr Ian R Holzman and the NICU staff at the Mount Sinai Medical Center for their assistance and support.

We also thank Tara Wilhelm Forstrom for her editorial assistance.

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