Indian Pediatrics 1998; 35:605-612 

COGNITIVE ABILITIES OF ASPHYXIATED SURVIVORS BEYOND 5 YEARS OF AGE

PERINATAL asphyxia is a major cause of morbidity and mortality in the first year of life. The survivors have long been recognized to have an increased risk of handicaps such as cerebral palsy, mental retardation, epilepsy, deafness and visual impairment in early childhood. However, with advances in perinatal care, there has been an increase in the non-impaired survivors.

The Apgar score(1) is widely accepted. as a means of assessing the severity of birth asphyxia. Several studies have shown a significant correlation between low Apgar score at one minute(2-5) and the incidence of neurological abnormality in survivors. These longitudinal studies have primarily focussed on motor sequelae and early developmental quotients. However, the out- come of unimpaired asphyxiated children has not been well documented in older children, particularly in the context of developing countries. These children are expected to have more school related difficulties as compared to normal children(6). This study was therefore designed to evaluate intellectual, psycho. educational and social maturity of survivors with moderate-severe asphyxia (Apgar ≤ 6 at 1 minute) beyond 5 years of age.

Subjects and Methods

The subjects were selected for evaluation from a cohort of term asphyxiated babies who were being followed longitudinally in the High Risk Clinic of our hospital. Entry criteria included term neonates who had an Apgar 6 at 1 minute and .were between 5 and 13 years without any physical, auditory or visual impairment at the time of selection. Twenty-seven of these were examined at a mean age of 7.2±1.6 years (Group 1) and 27 were examined at a mean age of 10.9±1.52 years (Group 2). Fifty 'seven non-asphyxiated healthy term infants, who were born and being followed in the Well Baby Clinic of the same hospital were selected as controls. The age at examination was comparable 10 that of the test subjects.

The assessment measures utilized for evaluating the cognitive abilities are summarized in Table I. The Indian adaptation of the Stanford Binet and the Vineland Social Maturity scale were used by us. The Raven's Progressive Matrices and the Bender Gestalt are performance tests and are culture free. The Wide Range Achievement Test was the only test used unadapted as there are no standardized tests available for reading, spelling and arithmetic for the Indian population. Six of the asphyxiated children and 7 of the controls could not perform this test as they were not well versed with the English language and were hence excluded from the analysis of this test.

All the psychometric tests were standardized and conducted with the help of one of the authors (VRN) who is a Child Psychologist. They were' administered to the children individually in a quiet room. , The entire assessment of a child took about Ph-2 hours. A few children had to be assessed on two or three different occasions. Family information of the, children included birth order, family size, level of maternal education, socio-economic status and school difficulties. The family information and the parent's questionnaires were administered by one of the authors (AT). Follow-up communication was through mailing to family, telephone calls or contact person.

Statistical Analyses

The cases and controls were compared with respect to all the outcome measures. Data was processed and analyzed on IBM compatible PC/XT using the EPI-Info Program. Differences in distribution were analyzed by Student's 't' test for normally distributed data or otherwise with Kruskal Wallis Test. Differences in proportion were analyzed by using the Chi-square test with Yate's correction or the Fisher Exact Test if the sample size was small.

Results

Profile of Subjects

A total of 54 asphyxiated and 57 control children participated in the study. Since the age range was wide, hence for the purpose of analysis, the asphyxiated and the control children were divided into two groups: (i) Group 1: tested at a mean a of 7.24±1.1 years (range 5-9 years); and (ii) Group 2: tested at a mean age of 10.9±1.22 years (range 9-13 years). Of the 54 asphyxiated children, 6 children had well controlled seizures and 1 child had arrested hydrocephalus at the time of enrollment.

TABLE I

Assessment Measures Utilized.

Table II shows the demographic data of both asphyxiated and control children. There were no significant differences in social class, maternal education, birth weight and gestation between the two groups.

Psychometric Tests

The results of these tests are summarized in Tables III & IV.

Group 1: On the tests of cognition, the asphyxiated children though scoring in the normal range did less well as compared to the control group. The mean IQ in the asphyxiated group was 106.7 as compared to 116.3 in controls (p<0.05). Nearly 19% of the asphyxiated children scored below the 25th centile in Raven's Progressive Matrices as compared to none of the controls. In the WRAT-R, the asphyxiated children did significantly less well as compared to the controls (p < 0.005). In the tests of motor function 41 %of the asphyxiated children showed the presence of non focal neurological signs as compared to 10% of controls (p < 0.05) and on the Bender Gestalt Test, 33% of the asphyxiated children performed in the abnormal range as compared to 7.1% of. controls (p<0.05). The mean social quotient of the asphyxiated children was 106.6 as compared to 117.6 in controls (p<0.005).
 

TABLE II
Demographic Data all Asphyxiated and Control Children.

Group 2: In the tests of cognition, the difference in the two groups was significant (p < 0.005). Thirty per cent of the asphyxiated children scored below the 25th centile on the Raven's Progressive Matrices as compared to 3.4% of controls (p < 0.05). In the WRA T - R also, the asphyxiated children were clearly disadvantaged in all the 3 subtests as compared to controls (p < 0.005). In the tests of motor functions 22% of the asphyxiated children had non focal neurological signs as compared to 3.4% of controls (p < 0.05) and about 48% performed in the abnormal range on the Bender Gestalt Test as compared to 21 % of controls (p<0.05). Similarly the mean social quotient of the asphyxiated children of Group 2 was significantly lower (p<0.005) as compared to the control children.

The distribution of Stanford Binet IQ scores for asphyxiated and control children is illustrated in Fig. 1. A higher proportion of asphyxiated children had an IQ of < 85 (< -1 S.D.) and fewer had IQ of > 115 (> + 1 S.D.) as compared to control children.

Discussion

This study gives the long term outcomes of asphyxiated children (APGAR Score ≤ 6) evaluated at mean age of 7.2 and 10.9 years. Earlier investigators have utilized a variety of laboratory and clinical criteria to make the diagnosis of asphyxia and study its outcome(5,6,14-20). However, amongst these the clinical categorization of neonatal encephalopathy associated with birth asphyxia(21) has been found to be a more helpful indicator of long term outcome (6,14,15). As our neonatal data pertains Apgar Score, we have analyzed accordingly.



 

Fig. 1. Distribution of Stanford Binet IQ scores in asphyxiated and control groups.

Our findings suggest that the non-impaired asphyxiated children as a group, perform in the normal range on tests of cognition, academic achievement and social maturity but comparison with socio-demographically matched control children reveals that they are significantly disadvantaged on nearly every measure tested. The findings of this study are consistent with previous reports of cognitive deficits and academic achievements(6,14- 17). Robertson et al.(6) reported that the mean IQ scores of non disabled survivors though in the normal range were significantly lower than the mean scores of the comparison group. Similar results were found in the St. Louis prospective study of anoxia(16). The same study(16) also reported that when 33 term 7 year old children who had perinatal anoxia were com- pared with controls, they had lower scores for vocabulary and perceptual motor measures but had normal scores for the Bender Gestalt Test and the Embedded Figure Test. Similar results have been reported by the Aberdeen study(18) and by Robertson et al.(15). These findings are comparable to those of our study where though a higher percentage of children performed in the abnormal range on the Bender Gestalt Test, the difference was not significant.

Follow-up studies of selected high risk populations have reported a higher proportion of minor neurological abnormalities in low birth weight infants(22) but with regards to asphyxia, the literature documents conflicting views(23-25). In the present study, a higher proportion of asphyxiated children were found to have "soft" neurological signs as compared to controls.

Although asphyxia per se is recognized as a significant perinatal risk factor, the interaction between asphyxia and adverse environmental factors has not been well established. Sameroff and Chandler(26) emphasize that a combination of perinatal risk factors and non-optimal rearing conditions can lead to poor developmental outcome whereas good rearing conditions can ameliorate the risk. In the present study, similarity in socio-economic and maternal education characteristics precluded an anlaysis of the influence of rearing conditions on developmental outcome amongst the asphyxiated and control children.

In conclusion, although the asphyxiated children performed in the normal range in various tests, in comparison to the control group they were clearly disadvantaged on nearly every measure tested. These children therefore tend to have a poor school performance and learning difficulties, for which they need to be referred for Special education. With a little extra help, early detection and modification of the home environment, these children can continue in normal schools and achieve better grades.

TABLE III

Results of Psychometric Tests

          * P < 0.05; ** P < 0.005; Values depict either Mean (SO), Number (%) or RR (95% CI).

TABLE IV

Results of Tests of Academic Achievement