Acta Pædiatrica ISSN 0803-5253
REGULAR ARTICLE
Children born extremely preterm show significant lower cognitive, language and motor function levels compared with children born at term, as measured by the Bayley-III at 2.5 years J M ansson ([email protected]), K Stjernqvist Department of Psychology, Lund University, Lund, Sweden
Keywords Bayley-III, Cognition, Developmental delay, Extremely preterm, Population-based study
ABSTRACT Aim: To assess developmental outcomes of children aged 2.5 years born extremely
Correspondence Johanna M ansson, Department of Psychology, Lund university, Box 213, SE-221 00 Lund, Sweden. Tel: + 46 (0)46 2228056 | Email: [email protected]
Methods: As a part of the population-based Extremely Preterm Infants in Sweden Study
Received 16 September 2013; revised 9 December 2013; accepted 29 January 2014. DOI:10.1111/apa.12585
preterm. (EXPRESS), 399 children born before 27 weeks of gestation and 366 control children born at term were assessed with the Bayley Scales of Infant and Toddler Development, third edition (Bayley-III), assigning scores for cognition, receptive and expressive communication, fine and gross motor functions. Based on control group means, prevalences of developmental delay in the preterm group were calculated. Mean score differences between subtests constituting the overall Bayley-III indices were analysed within both groups. Results: After controlling for socio-demographic, child and assessment variables, analyses showed significantly lower performances of the preterm group compared with the control group on the Bayley-III subtests. Prevalence of moderate–severe delay was 10.8% in cognitive, 14.9% in receptive communication, 14.5% in expressive communication, 12.4% in fine motor and 7.0% in gross motor functions. Significant differences between performances on subtests included in the same indices were detected. Conclusion: Extremely preterm children show significant lower cognitive, communicative and motor function levels at 2.5 years compared with children born at term. Bayley-III assessments permit the acquisition of nuanced information about development following extreme prematurity.
INTRODUCTION Extremely preterm birth – before 27 gestational weeks – is associated with substantial risks of deficits and difficulties later in life. Follow-up studies of extremely preterm infants report cognitive, neuromotor and communication disabilities as well as behavioural problems in early childhood and preschool years (1,2). Preterm birth is associated with poorer school performance compared with full-term classmates, and with increased risk of attention disorders (3–5). Children surviving extreme prematurity without major neonatal morbidities, with normal cognitive development, may display a variety of subtle learning and motor difficulties (6,7). Advances in neonatal care have resulted in increased survival rates among the most immature infants (8,9), although potentially with increased risk of disability
Key notes
Abbreviations Bayley-III, Bayley Scales of Infant and Toddler Development, third edition; EXPRESS, Extremely Preterm Infants in Sweden Study.
504
(3,10). As neonatal care is progressing, there is a continuous need for up-to-date estimates of short-term, mid-term and long-term outcomes after extreme prematurity, to provide a basis for treatment guidelines and parental counselling. The main objective of the population-based Extremely Preterm Infants Study in Sweden (EXPRESS) is to evaluate the consequences of extremely preterm birth. All infants
Developmental outcome at 2.5 years was assessed using the Bayley-III in a population-based cohort of children born extremely preterm in Sweden. Children born extremely preterm were at risk of delayed cognitive, receptive and expressive communication, and fine and gross motor functions compared with children born at term. Thorough and continuous follow-up of extreme prematurity regarding different developmental domains is necessary for adequate identification of deficits and for therapeutic interventions.
©2014 Foundation Acta Pædiatrica. Published by John Wiley & Sons Ltd 2014 103, pp. 504–511
M ansson and Stjernqvist
born before 27 gestational weeks in Sweden during a period of 3 years are included (9). The purpose of the present report is to assess the mid-term outcome of extreme prematurity, defined as cognitive, language and motor performance at 2.5 years of corrected age. Development is operationalised by the five subtests of Bayley Scales of Infant and Toddler Development, third edition (Bayley-III); Cognition, Expressive Communication, Receptive Communication, Fine Motor and Gross Motor (11). Our aim was to investigate group differences in Bayley-III subtest performances between children born extremely preterm and full term, exploring to what extent extreme prematurity is followed by mild, moderate or severe developmental delay at the age of 2.5 years. We also explore within-group patterns of performances on the subtests constituting the overall Bayley-III Index scales and compare performances on the communication and cognitive subtests.
METHODS Subjects During the 3-year period between April 1, 2004, and March 31, 2007, extensive perinatal data on all infants with a gestational age of 4, and matching for domicile, sex, day of birth and ethnicity. If the first set of parents declined participation, the second set was approached and so on, resulting in 366 control children being assessed. Bayley-III The Bayley Scales of Infant and Toddler Development, third edition (Bayley-III) is an individually administered instrument, designed to evaluate developmental functioning through a series of standardised test items. It quantifies cognitive, language and motor skills with children between the ages of one to 42 months (11). The previous version – Bayley-II – has been widely used internationally for clinical
Outcome of extreme prematurity at 2.5 years
assessments and research (13,14). The Bayley-II combined measures of both cognitive and language development, expressed as the Mental Developmental Index. Bayley-III separates the components of the Mental Developmental Index into two distinct scales; the Cognitive and Language Index scales. This revision led to the Cognitive Index being less dependent on language comprehension and expression (11). The Motor Index is equivalent to the Bayley-II Psychomotor Development Index. Bayley-III provides five subtests: Cognition, Receptive Communication, Expressive Communication, Fine Motor, and Gross Motor. Cognitive function includes sensorimotor development, concept formation and memory. Receptive Communication assesses word comprehension, the ability to respond appropriately to words and requests, whereas Expressive Communication measures preverbal communication, vocabulary and syntactic development. Fine Motor measures manipulation of objects and functional hand skills, whereas Gross Motor examines static positioning, movement of limbs and balance. Norm-referenced scaled scores can be calculated for all five subtests. The scaled scores are derived from the total raw scores and ranges from 1 to 19, with subtest means of 10 and standard deviations of 3. The Cognitive Index consists of the Cognitive subtest. The Expressive and Receptive Communication subtests constitute the Language Index. The Fine and Gross Motor subtests constitute the Motor Index. The Bayley-III has not yet been standardised in Sweden. Prevalences of developmental delay are typically based on the proportion of scores of more than one, two or three standard deviations below the reference mean, indicating mild, moderate and severe delay, respectively (15,16). Previous reports show that the Bayley-III has psychometric weaknesses that can affect scores (16,17). Anderson et al. (17) found that using normative criteria as reference resulted in unexpectedly low rates of delay in a group of extremely low birthweight and extremely preterm children. When using control group scores as reference, the proportions of delay rose to expectations. In this study, test scores were evaluated on the basis of the means and standard deviations of the controls. Function level was regarded as normal if the subtest scaled score was ≤+1 standard deviation and ≥ 1 standard deviation of the control mean. Procedure Participating children were assessed by clinical psychologists at perinatal centres around Sweden (Stockholm, Uppsala, Linkoping, Lund, Gothenburg, Orebro and Umea). Prior to data collection, the psychologists were trained in the Bayley-III instrument by one of the authors (KS), who also were available for online supervision during the data collection period. The Bayley-III assessment was completed during one occasion. The intention was that children with a foreign native language would be tested with the assistance of a professional interpreter. If no professional interpreter was available, the accompanying parent served as interpreter. For the extremely preterm group, the assessment was included in a clinical follow-up.
©2014 Foundation Acta Pædiatrica. Published by John Wiley & Sons Ltd 2014 103, pp. 504–511
505
M ansson and Stjernqvist
Outcome of extreme prematurity at 2.5 years
Sometimes examiners had met the children during their stay at the neonatal intensive care unit. Thus, it was not possible for the examiners to be blinded to the group status extremely preterm/full term. Follow-up ended in February 2010 as the last child reached 2.5 years. The study was approved by the Regional Ethics Review Board at Lund University (Dnr 469/2007). All parents provided written consent for the examination. Statistical methods Categorical data were compared using chi-square tests. Independent samples t-tests were conducted to compare Bayley-III subtest mean scores between children born extremely preterm and controls, and to compare nonSwedish-speaking children tested with vs. without the assistance of a professional interpreter. A general linear model was used to compare mean differences in Bayley-III subtest scores between the preterm group and control group, when adjusting for parental educational level, maternal age and maternal country of birth (parental variables), native language (child variable), assessment with interpreter and geographical perinatal centre (assessment variables). Effect sizes were calculated in terms of Cohen’s d, defined by the difference between two means divided by the pooled standard deviation of those means. Cohen’s guidelines were followed to indicate the strength of the effect sizes, with 0.20, 0.50 and 0.80 referring to small, medium and large effect size, respectively (18). Based on subtest means and standard deviations of the control group, the test scores were classified as being (i) ≤ mean +1 standard deviation and ≥ mean 1 standard deviation; (ii)
REGULAR ARTICLE
Children born extremely preterm show significant lower cognitive, language and motor function levels compared with children born at term, as measured by the Bayley-III at 2.5 years J M ansson ([email protected]), K Stjernqvist Department of Psychology, Lund University, Lund, Sweden
Keywords Bayley-III, Cognition, Developmental delay, Extremely preterm, Population-based study
ABSTRACT Aim: To assess developmental outcomes of children aged 2.5 years born extremely
Correspondence Johanna M ansson, Department of Psychology, Lund university, Box 213, SE-221 00 Lund, Sweden. Tel: + 46 (0)46 2228056 | Email: [email protected]
Methods: As a part of the population-based Extremely Preterm Infants in Sweden Study
Received 16 September 2013; revised 9 December 2013; accepted 29 January 2014. DOI:10.1111/apa.12585
preterm. (EXPRESS), 399 children born before 27 weeks of gestation and 366 control children born at term were assessed with the Bayley Scales of Infant and Toddler Development, third edition (Bayley-III), assigning scores for cognition, receptive and expressive communication, fine and gross motor functions. Based on control group means, prevalences of developmental delay in the preterm group were calculated. Mean score differences between subtests constituting the overall Bayley-III indices were analysed within both groups. Results: After controlling for socio-demographic, child and assessment variables, analyses showed significantly lower performances of the preterm group compared with the control group on the Bayley-III subtests. Prevalence of moderate–severe delay was 10.8% in cognitive, 14.9% in receptive communication, 14.5% in expressive communication, 12.4% in fine motor and 7.0% in gross motor functions. Significant differences between performances on subtests included in the same indices were detected. Conclusion: Extremely preterm children show significant lower cognitive, communicative and motor function levels at 2.5 years compared with children born at term. Bayley-III assessments permit the acquisition of nuanced information about development following extreme prematurity.
INTRODUCTION Extremely preterm birth – before 27 gestational weeks – is associated with substantial risks of deficits and difficulties later in life. Follow-up studies of extremely preterm infants report cognitive, neuromotor and communication disabilities as well as behavioural problems in early childhood and preschool years (1,2). Preterm birth is associated with poorer school performance compared with full-term classmates, and with increased risk of attention disorders (3–5). Children surviving extreme prematurity without major neonatal morbidities, with normal cognitive development, may display a variety of subtle learning and motor difficulties (6,7). Advances in neonatal care have resulted in increased survival rates among the most immature infants (8,9), although potentially with increased risk of disability
Key notes
Abbreviations Bayley-III, Bayley Scales of Infant and Toddler Development, third edition; EXPRESS, Extremely Preterm Infants in Sweden Study.
504
(3,10). As neonatal care is progressing, there is a continuous need for up-to-date estimates of short-term, mid-term and long-term outcomes after extreme prematurity, to provide a basis for treatment guidelines and parental counselling. The main objective of the population-based Extremely Preterm Infants Study in Sweden (EXPRESS) is to evaluate the consequences of extremely preterm birth. All infants
Developmental outcome at 2.5 years was assessed using the Bayley-III in a population-based cohort of children born extremely preterm in Sweden. Children born extremely preterm were at risk of delayed cognitive, receptive and expressive communication, and fine and gross motor functions compared with children born at term. Thorough and continuous follow-up of extreme prematurity regarding different developmental domains is necessary for adequate identification of deficits and for therapeutic interventions.
©2014 Foundation Acta Pædiatrica. Published by John Wiley & Sons Ltd 2014 103, pp. 504–511
M ansson and Stjernqvist
born before 27 gestational weeks in Sweden during a period of 3 years are included (9). The purpose of the present report is to assess the mid-term outcome of extreme prematurity, defined as cognitive, language and motor performance at 2.5 years of corrected age. Development is operationalised by the five subtests of Bayley Scales of Infant and Toddler Development, third edition (Bayley-III); Cognition, Expressive Communication, Receptive Communication, Fine Motor and Gross Motor (11). Our aim was to investigate group differences in Bayley-III subtest performances between children born extremely preterm and full term, exploring to what extent extreme prematurity is followed by mild, moderate or severe developmental delay at the age of 2.5 years. We also explore within-group patterns of performances on the subtests constituting the overall Bayley-III Index scales and compare performances on the communication and cognitive subtests.
METHODS Subjects During the 3-year period between April 1, 2004, and March 31, 2007, extensive perinatal data on all infants with a gestational age of 4, and matching for domicile, sex, day of birth and ethnicity. If the first set of parents declined participation, the second set was approached and so on, resulting in 366 control children being assessed. Bayley-III The Bayley Scales of Infant and Toddler Development, third edition (Bayley-III) is an individually administered instrument, designed to evaluate developmental functioning through a series of standardised test items. It quantifies cognitive, language and motor skills with children between the ages of one to 42 months (11). The previous version – Bayley-II – has been widely used internationally for clinical
Outcome of extreme prematurity at 2.5 years
assessments and research (13,14). The Bayley-II combined measures of both cognitive and language development, expressed as the Mental Developmental Index. Bayley-III separates the components of the Mental Developmental Index into two distinct scales; the Cognitive and Language Index scales. This revision led to the Cognitive Index being less dependent on language comprehension and expression (11). The Motor Index is equivalent to the Bayley-II Psychomotor Development Index. Bayley-III provides five subtests: Cognition, Receptive Communication, Expressive Communication, Fine Motor, and Gross Motor. Cognitive function includes sensorimotor development, concept formation and memory. Receptive Communication assesses word comprehension, the ability to respond appropriately to words and requests, whereas Expressive Communication measures preverbal communication, vocabulary and syntactic development. Fine Motor measures manipulation of objects and functional hand skills, whereas Gross Motor examines static positioning, movement of limbs and balance. Norm-referenced scaled scores can be calculated for all five subtests. The scaled scores are derived from the total raw scores and ranges from 1 to 19, with subtest means of 10 and standard deviations of 3. The Cognitive Index consists of the Cognitive subtest. The Expressive and Receptive Communication subtests constitute the Language Index. The Fine and Gross Motor subtests constitute the Motor Index. The Bayley-III has not yet been standardised in Sweden. Prevalences of developmental delay are typically based on the proportion of scores of more than one, two or three standard deviations below the reference mean, indicating mild, moderate and severe delay, respectively (15,16). Previous reports show that the Bayley-III has psychometric weaknesses that can affect scores (16,17). Anderson et al. (17) found that using normative criteria as reference resulted in unexpectedly low rates of delay in a group of extremely low birthweight and extremely preterm children. When using control group scores as reference, the proportions of delay rose to expectations. In this study, test scores were evaluated on the basis of the means and standard deviations of the controls. Function level was regarded as normal if the subtest scaled score was ≤+1 standard deviation and ≥ 1 standard deviation of the control mean. Procedure Participating children were assessed by clinical psychologists at perinatal centres around Sweden (Stockholm, Uppsala, Linkoping, Lund, Gothenburg, Orebro and Umea). Prior to data collection, the psychologists were trained in the Bayley-III instrument by one of the authors (KS), who also were available for online supervision during the data collection period. The Bayley-III assessment was completed during one occasion. The intention was that children with a foreign native language would be tested with the assistance of a professional interpreter. If no professional interpreter was available, the accompanying parent served as interpreter. For the extremely preterm group, the assessment was included in a clinical follow-up.
©2014 Foundation Acta Pædiatrica. Published by John Wiley & Sons Ltd 2014 103, pp. 504–511
505
M ansson and Stjernqvist
Outcome of extreme prematurity at 2.5 years
Sometimes examiners had met the children during their stay at the neonatal intensive care unit. Thus, it was not possible for the examiners to be blinded to the group status extremely preterm/full term. Follow-up ended in February 2010 as the last child reached 2.5 years. The study was approved by the Regional Ethics Review Board at Lund University (Dnr 469/2007). All parents provided written consent for the examination. Statistical methods Categorical data were compared using chi-square tests. Independent samples t-tests were conducted to compare Bayley-III subtest mean scores between children born extremely preterm and controls, and to compare nonSwedish-speaking children tested with vs. without the assistance of a professional interpreter. A general linear model was used to compare mean differences in Bayley-III subtest scores between the preterm group and control group, when adjusting for parental educational level, maternal age and maternal country of birth (parental variables), native language (child variable), assessment with interpreter and geographical perinatal centre (assessment variables). Effect sizes were calculated in terms of Cohen’s d, defined by the difference between two means divided by the pooled standard deviation of those means. Cohen’s guidelines were followed to indicate the strength of the effect sizes, with 0.20, 0.50 and 0.80 referring to small, medium and large effect size, respectively (18). Based on subtest means and standard deviations of the control group, the test scores were classified as being (i) ≤ mean +1 standard deviation and ≥ mean 1 standard deviation; (ii)
