The aim of this study was to determine the expressive vocabulary of children with hearing loss (HL) enrolled in early intervention (EI) ⩽3 vs >3 months in the first 24 months and to compare with hearing controls. It was hypothesized that the number of words produced would be higher for children with HL enrolled in EI ⩽3 vs >3 months.
This is a prospective longitudinal matched cohort study.
The children with HL produced fewer words than the children with hearing. In addition, children with HL enrolled in EI ⩽3 months had a larger expressive vocabulary percentile score compared with children with HL enrolled >3 months. Children with mild HL enrolled in EI ⩽3 months had the greatest growth in vocabulary between 12 to 16 and 18 to 24 months.
Although multiple factors are associated with expressive vocabulary growth of children with HL, enrollment in EI ⩽3 months has sustained beneficial effects on expressive vocabulary at 18 to 24 months.
As a result of newborn hearing screening, evidence has accumulated for the importance of early enrollment in early intervention (EI) to improve the outcomes of children with hearing loss (HL).1, 2, 3, 4, 5, 6 We previously reported the beneficial effects of very early enrollment (⩽3 months) in EI for infants with HL on language outcomes at 12 to 16 months of age.7 In addition, the children with bilateral moderate to profound HL lagged behind the children with mild HL and hearing peers in early receptive and expressive language. Our findings at 12 to 16 months support the findings of others that EI provides beneficial effects for children with HL,2, 3, 7 and that all degrees of HL including bilateral moderate, severe and profound HL8, 9, 10, 11, 12 and unilateral or mild HL (⩽40 dB) have an impact on communication skills and language outcomes.12, 13, 14, 15, 16, 17, 18
Vocabulary size and timing of fast word learning are important predictors of subsequent language milestones.19, 20 Children with HL with hearing parents typically have difficulty acquiring new words, either spoken or signed, and require both visual and auditory clues to meaning.21 Early EI enrollment may facilitate vocabulary development by increasing the accessibility of input through early amplification and through teaching families ways of modifying their input to match their toddlers’ needs.
The objective of this report was to assess the changes in vocabulary (either signed or spoken) between 12 to 16 and 18 to 24 months of children with HL compared with hearing children. A second objective was to evaluate the effects of age of entry into EI and degree of HL. The primary hypotheses at 18 to 24 months were: (1) Children with HL will have fewer words compared with hearing controls; (2) Children with HL who start EI services by 3 months of age will have larger expressive vocabularies than children with HL who start EI after 3 months; and (3) Children with all degrees of HL who receive EI services by 3 months will have greater growth in vocabulary between 12 to 16 and 18 to 24 months compared with children enrolled after 3 months.
This is a prospective study of the language outcomes of infants identified in the Rhode Island newborn screening program who were born between 15 October 2002 and 31 January 2005. The cohort that has been described7, 22 consists of infants screened in either the Neonatal Intensive Care Unit (NICU) or well baby nursery and diagnosed with congenital HL and matched hearing controls who passed the newborn screen. Matches for each infant with HL included two to three infants who passed the standard hearing screen. Matches were based on a hierarchical matching procedure for the following characteristics: gender, date of birth ±90 days, hospital of birth, normal nursery vs NICU, maternal education, race/ethnicity, and health insurance. When necessary to find sufficient matches, matching criteria was relaxed for the following factors: maternal education, race/ethnicity and health insurance.
Enrollment procedures were previously described.7, 22 Eligible children diagnosed with all degrees of congenital HL were sequentially identified in the Rhode Island Hearing Assessment database and all families were approached for consent. Parents of 31 of 56 (55%) eligible infants consented to participate. A comparison of infants enrolled with those not enrolled revealed no differences in gender, NICU vs well baby nursery, primary language English, or private vs public health insurance. Enrolled infants with HL were more likely to be of very low birth weight than those not enrolled (48 vs 17%, respectively; P<0.01). The Institutional Review Board approval was obtained.
Children identified with permanent HL were referred simultaneously to standard Part C EI and the Family Guidance Program, a statewide specialty program for infants and toddlers with HL, which supports the early language acquisition needs unique to infants and young children with HL, and the modality choices identified by each family. The Part C program provides occupational therapy, physical therapy, and additional speech therapy services as needed for children with comorbidities. On receiving a referral and diagnosis, the Family Guidance staff initiated contact and home visits within a week of the referral date.
This report covers data collected at 18 to 24 months and the change in the size of early expressive vocabularies of children between 12 to 16 and 18 to 24 months. Demographic information, interim history and socioeconomic status data23 were collected. As some of the infants with HL were one of a set of twins or triplets and their siblings with no HL were enrolled as control matches, all mothers of multiples completed separate interviews for each child.
The MacArthur-Bates Communicative Development Inventory (MCDI)24 was completed by mothers at both 12 to 16 and 18 to 24 months. The MCDI prompts parents to record their child's understanding and use of early vocabulary items separated into word categories. Parents are asked to identify the words or signs that their child has been observed to use. The MCDI has been normed and validated. Studies on the validity of the MCDI for children with language impairments and for children with HL have found that parent reports show high concurrent validity with other measures of early language.25, 26 The MCDI: Words and Gestures was administered at 12 to 16 months.7 At 18 to 24 months, the MCDI: Words and Sentences, which consists of two parts, ‘Part 1: Words Children Use’, which includes a 680-word vocabulary list, and ‘Part II: Sentences & Grammar’, which includes questions on word endings, word forms, word combinations and sentence complexity, was administered.
As Words Produced is part of the MCDI for both 12 to 16 and 18 to 24 months, analyses were conducted to assess change over time of Words Produced and Words Produced percentile scores. The MCDI was administered to all English-speaking families and a normed Spanish version was administered to native Spanish speakers. If signed vocabulary was understood or used, it was counted accordingly. The American Sign Language (ASL) version was used with the one family that used ASL at home. Scores are reported separately for this family, as ASL norms and percentiles are still in development, and for two control families whose primary languages at home were Mandarin and Fulani.
This was a matched cohort study. Between-group analysis (HL vs control) was performed using t-tests on continuous variables and χ2 on categorical variables. Variables that demonstrated significant skew and/or sufficiently differing between-group variances were log transformed to normalize the data for parametric analyses. To test the impact of age of entry into EI, the children with HL were divided into two groups: children with entry into EI ⩽3 months vs >3 months. In addition, the effects of degree of HL: moderate to profound HL (>40 dB) and mild HL (⩽40 dB or unilateral HL of any degree) were examined. Analyses were also performed to examine the change in number of words produced between 12 to 16 and 18 to 24 months.
In all, 31 children with HL and 92 hearing children enrolled in the study were evaluated at 12 to 16 and/or 18 to 24 months. Characteristics of the mothers and children in the HL and hearing control groups are shown in Table 1. Mothers of children in the HL and control groups were similar in maternal age, marital status, education, insurance status and primary language spoken in the home. Children with HL were more likely to be of very low birth weight compared with controls (48 vs 20%, respectively; P=0.0017). One mother of a child with HL was culturally deaf. The Hollingshead socioeconomic status score was 6.7 points higher for mothers of children with hearing compared with mothers of children with HL. Child's gender and race were similar across groups with racial demographics representative of Rhode Island. There was a trend for more preterm children in the HL group. Of the 31 children with HL, 13 have mild HL (11 unilateral and 2 mild bilateral ⩽40 dB, per best ear) and 18 have bilateral moderate to profound HL (>40 dB). No child had a cochlear implant at the time of the 18- to 24-month assessment. Median age of amplification for the children with bilateral moderate to severe to profound HL was 5.9 months with a range of 2.6 to 21.7. One infant using ASL was not amplified. In contrast, median age for the infants with mild or unilateral loss was 13.4 months with a range of 6.2 to 48. Both children with mild bilateral loss were amplified close to 6 months of age. Six parents of children with unilateral loss did not choose amplification and the remainder tended to make the decision once the child had evidence of a language delay.
The parents of 78% of our children with HL incorporated some sign into daily communication with their children over the first 2 years of life, whereas 22% choose purely auditory–oral methods. Only one family used ASL exclusively. In all, 94% of children with HL and 31% of controls received EI services. The majority of children with HL received both generalized Part C EI and specialized services from Family Guidance. Two families of children with unilateral HL opted not to participate in any form of EI and were categorized in the EI >3 months group for analytical purposes. The analyses were repeated excluding the two children who did not participate in EI and the results remained unchanged (not shown). The frequency of visits from Family Guidance specialized services for the children in EI ⩽3 months was 1.9 visits per month (range 0.3 to 4) and the frequency of children in EI >3 months was 2.5 visits per month (range 1 to 4, P=0.1224). The frequency of EI visits by degree of HL was 2.7 visits per month (range 1 to 4) for children with moderate to profound HL and 1.1 visits per month (range 0.3 to 2 visits, P=0.0003), respectively, for children with mild HL. All families of children with HL enrolled in EI participated until the age of 3 years.
By 18 to 24 months, 10 (32%) of the 31 children with HL had been diagnosed with a neurodevelopmental comorbidity (one partial trisomy 2p, one Nager Syndrome, five children with moderate-to-severe cerebral palsy, one with pervasive developmental disorder, one with microcephaly, and one with severe chronic lung disease and a tracheostomy). None of the controls had severe neurodevelopmental comorbidity. One infant with comorbidity (severe chronic lung disease and a tracheostomy) was not seen at 18 to 24 months.
Scores on the Words Produced section and Total Gestures section (indicator of nonverbal cognitive skills) of the MCDI for both the HL and hearing control groups at 12 to 16 months are shown in Table 2. Of the children with HL, 50% had scores <10th percentile for total gestures compared to 31% of children with hearing. We reanalyzed the study groups after excluding children with comorbidities for Total Gestures <10th percentile. The scores of the HL and control children were similar at 32 vs 31% P=0.983, respectively (not shown in table). At both 12 to 16 and 18 to 24 months, children with HL had fewer Words Produced, lower Words Produced percentiles, and were more likely to have scores below the 10th percentile than children with hearing. In addition, children with HL scored lower than hearing children on almost all subtests of the MCDI. Scores for Words Produced and Words Produced percentile at 18 months were reanalyzed excluding the children who had comorbidities, and although group differences persisted between HL and hearing children, they were diminished (95.3±127 vs 150.3±144, P<0.04 and 22±26 vs 35±28, P<0.03, respectively). Analyses were repeated for Words Produced and Words Produced percentile covarying for socioeconomic status, and significance remained unchanged (data not shown).
Scores are not included in analyses for one child in the moderate to profound group whose family communicates in ASL, one control child whose primary language is Mandarin, and one control whose native language is Fulani. The mother of the child using ASL reported that her child understood 43 ASL signs, produced 26 ASL signs and 24 gestures at 12 to 16 months, and produced 256 signs with a mean length of utterance of 2.7 signs at 18 to 24 months. The mother of the child speaking Mandarin reported that her child understood 41 words, produced 2 words, and used 21 gestures at 12 to 16 months, and produced 177 words at 18 to 24 months with a 1.3 mean of three longest utterances. The Fulani family was only seen at 18 to 24 months, and the mother reported that the child produced 24 words without combining words into utterances.
The data for the children with HL were analyzed relative to age of entry to EI (Table 3). Words Produced trended higher (110.5 vs 33.4, P=0.19) and Words Produced percentile was higher at 18 to 24 months (27.1±29.2 vs 7.2±5.9; P=0.01) for children with HL enrolled in EI ⩽3 months vs >3 months, respectively. Children enrolled in EI ⩽3 months were also less likely to be performing below the 10th percentile for Words Produced (42.9 vs 93.9%, P=0.003). Despite gains in number of words produced between 12 to 16 and 18 to 24 months, Words Produced percentile decreased for both groups of children with HL. We repeated the analyses for words produced omitting the two children who were not enrolled in EI and the group differences in Words Produced percentile remained unchanged (EI yes vs no; 27th percentile vs 7th percentile, P<0.0009).
We analyzed for effects of degree of HL. Children with moderate to profound HL enrolled in EI ⩽ 3months had a higher Words Produced percentile at 12 to 16 (39.8±23 vs 8.9±8; P<0.004) and 18 to 24 months (15.0±9 vs 5.4±2; P<0.04) than those enrolled >3 months. Although the percentiles trended higher for infants with mild HL, they did not reach significance. However, children with mild HL enrolled in EI ⩽3 months had the greatest growth in words produced between 12 to 16 and 18 to 24 months (142±161 words) and children with moderate to profound HL enrolled in EI >3 months had the slowest growth (22±29 words).
Figure 1 displays graphically the association of degree of HL, symbolic gestures percentile as an indicator of nonverbal intelligence, the presence of comorbidities, very low birth weight, and age of entry to EI with Words Produced percentile scores at 18 to 24 months. All child factors were associated with lower Words Produced percentile, whereas early age of entry to EI was associated with higher Words Produced percentile.
Our findings support our primary hypothesis that children with HL have smaller expressive vocabularies and lower Words Produced percentile scores compared with hearing controls at 18 to 24 months. As our cohort of infants born in Rhode Island was enrolled shortly after the newborn hearing screening and diagnostic assessment, it is representative of a typical population of children identified with HL as a result of universal newborn screening. In all, 63% of the children with HL were cared for in an NICU and 50% had a Total Gestures score below the 10% (as an indicator of low cognitive function). By 18 to 24 months, the presence of a neurodevelopmental comorbidity had been identified in 10 of 31 (32%) children with HL. This is consistent with the literature of increased comorbidity among children with HL. Only the subgroup of children with mild bilateral or unilateral HL who had 12 to 16 month total gestures scores >10th percentile and were enrolled in EI ⩽3 months had 18 to 24 month Words Produced percentile scores similar to hearing children.
Our second hypothesis was that children with HL enrolled in EI ⩽3 months have better vocabulary skills at 18 to 24 months of age compared with children enrolled >3 months. Analyses demonstrated the beneficial effects of EI ⩽3 months for the total cohort of children with HL with trends for benefit for the subgroups of children with moderate to profound HL and mild HL. Beneficial effects were also identified for children with HL without comorbidities. Several retrospective and prospective studies have evaluated the effects of EI for children with HL.1, 2, 3, 4, 5, 6 Better language outcomes have previously been reported for deaf and hard-of-hearing children who received EI by 11 months.2 Yoshinaga-Itano et al.1 demonstrated language benefits in children identified with HL before 6 months with all degrees of HL, both with and without disabilities. Our 18 to 24 month findings for children without comorbidities who had EI services ⩽3 months are similar to the findings of Yoshinaga-Itano et al.1at 31 to 36 months of age. Children with HL without comorbidities enrolled in EI ⩽3 months vs >3 months produced more words (123±156 vs 53±43, respectively) (not shown). This lack of significance may be secondary to the sample size and some skewing of the data. Mean Words Produced scores for children with HL without comorbidities enrolled in EI ⩽3 months (123±156), however, are similar to the hearing controls (150±144). This is similar to the findings of Yoshinaga-Itano.
Greater degree of HL was associated with lower expressive vocabulary in our cohort. Although our children with mild or unilateral HL have vocabularies similar to hearing controls at 18 to 24 months, the impact13, 14 of mild sensorineural HL (15 to 40 dB) at older ages can be substantial. Children with unilateral loss are more likely to fail a grade in school,18 and children with mild bilateral HL and unilateral HL have more articulation problems.17 Delays have been reported in speech–language, cognition, vocabulary, verbal ability and reasoning among children with unilateral HL.12, 13, 14, 15, 16, 17 Findings of suboptimal academic skills have been reported in school age children with mild bilateral HL.27, 28, 29, 30, 31, 32, 33, 34, 35 Other investigators have reported delayed development of vocabulary and speech skills in children with unilateral HL.36, 37 Although it has been reported that children with unilateral right-sided HL have poorer performance on verbal tests than children with left ear unilateral HL,16 our cohort was too small and diverse to test this hypothesis. In addition, difficulties most likely occur later in the developmental trajectory, when acquiring more complex words for success in school.
Our third hypothesis was that children with all degrees of HL enrolled in EI by 3 months would have greater growth in expressive vocabulary between 12 to 16 and 18 to 24 months compared with infants enrolled >3 months. Although all study groups increased their vocabulary size between 12 to 16 and 18 to 24 months, children with HL enrolled in EI >3 months had the slowest growth. The rate of vocabulary growth for children with moderate to profound HL enrolled in EI >3 months was slower than all other groups. This difference was present even after excluding children with comorbidities. This suggests persisting negative effects of later onset of intervention on vocabulary skills, particularly for children with moderate to profound HL, and supports the importance of birthing hospital and NICU staff conveying the results of the newborn screen to the family and PCP.
An important finding was that vocabulary growth for children with HL did not continue at the same rate as controls. Although the hearing control group maintained their average percentile for words produced between 12 to 16 and 18 to 24 months, children with HL dropped their percentile rating. This indicates that for children with HL, the rapid early vocabulary learning observed for hearing children is delayed or may not occur as part of their developmental trajectories. The single exception was the children with mild HL enrolled in EI ⩽3 months; their vocabulary growth was similar to hearing controls. Comparable findings have been reported by others.38, 39 Moeller reported vocabulary scores at 16 and 24 months for a cohort of 112 children with bilateral mild to profound sensorineural HL. Vocabulary scores increased with age but at a slower rate for children with HL than the hearing children. A similar trajectory of expressive vocabulary development for children with HL was reported by Mayne et al.40 Their study provided information on expressive vocabulary using the MCDI for children with HL ranging from mild to profound, who were identified by 6 months of age. Size of vocabulary was significantly affected by both age of identification (before vs after 6 months old) and cognitive impairments (<80 cognitive quotient).
In addition to vocabulary growth, other critical language skills that co-occur during this developmental period were assessed by the MCDI at 18 to 24 months and were delayed for children with HL. While learning new words, children are also learning how to use words to talk about absent objects, and what to add to these words such as using word endings. All these dimensions must emerge synchronically for children to begin producing more complex language. Significant differences in this cohort compared with hearing controls in acquiring not only number of words but also word use in sentences points to the challenges all children with HL face in the acquisition process.
The strengths of this prospective study are as follows: (1) This is a longitudinal cohort with good compliance for follow-up; (2) standardized assessments were completed; and (3) effects of EI and degree of HL are assessed. Weaknesses include (1) limited sample size of children with HL and (2) observational study design.
In summary, our findings provide evidence for the continued beneficial effects of early enrollment (⩽3 months) in EI on early language outcomes of young children with HL. Although children with all degrees of HL derive benefit from specialized intervention programs, which meet their developmental needs and optimize communicative outcomes,1, 3, 41 the course of their development is highly variable showing wide individual differences. Despite the fact that multiple nonmodifiable child factors, including degree of HL, presence of a comorbidity and nonverbal intelligence, contribute to language outcomes, early enrollment in EI has sustained beneficial effects on expressive vocabulary at 18 to 24 months. Identifying early word production needs for children with HL allows service providers to focus on specific learning experiences and interactions that optimize language outcomes for children and their families.
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We express our appreciation to Joyce Rose for paper preparation, and the families that generously gave their time to participate in this study. This study was funded by a Cooperative Agreement from the Centers for Disease Control & Prevention, # UR3/CCU120033-01 and the Association of University Centers on Disabilities # AUCD-RTOI 2006-06-07-1.
The authors declare no conflict of interest.
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Vohr, B., Jodoin-Krauzyk, J., Tucker, R. et al. Expressive vocabulary of children with hearing loss in the first 2 years of life: impact of early intervention. J Perinatol 31, 274–280 (2011). https://doi.org/10.1038/jp.2010.110
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