Introduction

In the first week of life, high bilirubin level is an important indicator because free bilirubin can cross the blood brain barrier. It is well known that bilirubin causes serious brain damage when it attains very high levels. Damage to the central nervous system varies depending on the bilirubin level. This neurological effect has a broad spectrum, from mild impacts such as isolated auditory neuropathy, movement disorders, dystonia, cognitive disorders, mild mental retardation to much more severe impacts such as severe neuromotor deficits due to acute bilirubin encephalopathy and auditory sequelae (1-3).

Today, most patients with high bilirubin levels do not experience neurological damage due to the modern treatment methods and because patients can benefit more from medical services (4,5). However, there are few patients who still develop mild neurological damage, and detecting these patients is critical. Essentially, the population in which we can make a difference is among patients with little damage. Therefore, in addition to the hearing assessment, which is usually what we pay the most attention to during follow-up, neurodevelopmental screening tests should be carried out diligently (6-8).

In our study, we made a neurodevelopmental evaluation of newborns with different bilirubin levels. We used the Denver II Developmental Screening test (DDST), which included personal-social, fine motor, language and gross motor assessments.

Methods

This prospective and comparative study was approved by the local ethics committee (approval number: GOKAEK/2017-550, date: 08.02.2017). All the participants were informed verbally and in writing about the study and their written consents were obtained.

Study Groups

The study included two groups: study group and control group. The study group consisted of 48 cases who were treated for a high bilirubin (total bilirubin) level (>22 mg/dL) and were born at 38 to 42 gestational weeks. Seventy-seven patients who were treated in our neonatal intensive care unit due to hyperbilirubinemia between 2015 and 2016 (>22 mg/dL) were identified. Those who were reachable by phone were included in the study. The control group consisted of 50 healthy children who visited our outpatient clinic. Exclusion criteria included preterm births (<38 weeks), hypoxic delivery, intrauterine growth retardation, major congenital malformation, hospitalisation for any reason, hearing problems, any chronic disease and maternal disease during pregnancy.

Detailed physical examinations and neurological examinations of the children were performed. Weight, height and body mass index (BMI) of all the cases were recorded. Mothers were asked if they gave their children iron prophylaxis between 4 and 12 months. Children’s Hearing tests (Brain stem evoked response audiometry - BERA) were performed. The hospitalisation files of the children in the study group were examined and the data were recorded. Socio-demographic data of the parents was also obtained.

Neurodevelopmental Assessment

DDST was used in the neurodevelopmental evaluation of the patients. The same paediatrician who had the certificate evaluated all the children. Denver developmental screening test, which was defined by Frankenburg and Dodds in 1967, was revised in 1990 as Denver II. In our study, we used the version of this test standardised by Yalaz et al. (9) in 2009.

DDST is applied to 0-6 years old children with a healthy appearance. It consists of 134 items created to evaluate the ability in 4 developmental areas according to age: personal-social (21 items), fine motor (33 items), language (42 items) and gross motor (38 items). The test results in 4 possible evaluations: normal, abnormal, suspicious and non-testable.

Statistical Analysis

The Shapiro-Wilk test was used to perform normality control on the histogram, Q-Q plot and box plot charts. Data were expressed as median, minimum, maximum, frequency and percentage. The measurement variables between the two groups were analysed with the Mann-Whitney U test. Receiver operating characteristic (ROC) analysis was performed. Diagnostic tests (sens., Spe., PPV, NPV, Accuracy) and 95% confidence intervals were given. Nominal variables were evaluated with Yates corrected chi square test with Yates correction and Fisher’s exact probability tests. Odds ratio values and 95% confidence intervals were calculated. The limit of significance was taken as p<0.05 and bidirectional. The analyses were performed using NCSS 10 (2015. Kaysville, Utah, USA) software program.

Results

This study included 48 newborns with hyperbilirubinaemia and 50 healthy children. There was no significant difference between the hyperbilirubinaemia and control groups in terms of the female/male ratio (p=0.54). The average age in the study group was 37.3±8.3 months, the average weight was 14.8±2.6 kg, the average height was 100.2±7.2 cm, and the average BMI was 14.8±1.1. The mean age in the control group was 41.7±10.2 months, the average weight was 14.6±2.2 kg, the average height was 101.8±6.8 cm, and the average BMI was 14.1±1.1. In terms of age, weight, height and BMI, no significant difference was found between the study and control groups (p=0.14), (p=0.66), (p=0.42) and (p=0.13), respectively. There was no difference between the use of iron prophylaxis in both groups (p=0.85) (Table 1).

Hospital records of the children in the hyperbilirubinaemia group were examined. The average gestational age was 38.7±0.4 weeks, mean birth weight was 3185±335 g and the duration of hospitalisation was 3.22±1.4 days. The time of admission was found to be 4.3±2.4 days after birth. The cause of hyperbilirubinaemia was ABO incompatibility in 17 patients, Rh incompatibility in 4 patients, G6PDH deficiency in 5 patients and weight loss in 3 patients. The cause of the hyperbilirubinaemia was not found in 19 patients. Blood exchange was performed in 2 patients, IVIG treatment was applied to 9 patients, and phototherapy was given to all the patients.

The maternal and paternal demographic data of the study and control groups were compared. No statistically significant difference was found between the two groups in terms of maternal and paternal age and education level, number of children in the family and monthly income (Table 2).

DDST general results were evaluated. There was a statistically significant difference between the two groups in terms of neurodevelopment. Neurodevelopment was significantly lower in the hyperbilirubinaemia group (p<0.001) (Table 3).

DDST results were evaluated according to developmental areas. There was no statistical difference in the personal-social (p=0.26) and gross motor (p=0.31) areas in both groups. In the hyperbilirubinaemia group, the developmental delay was statistically significant in the language and fine motor areas (p<0.001), (p=0.046) respectively (Table 4).

ROC curve analysis was performed to determine the cut-off value of total bilirubin in predicting developmental delay. Total bilirubin cut-off value was found to be 23.5 mg/dL (p=0.009) (Figure 1).

Discussion

Hyperbilirubinaemia, one of the most common problems of the neonatal period, is critical because it affects brain development when the bilirubin level exceeds a certain threshold value.

Bilirubin toxicity has been associated with many conditions such as neurodevelopmental delays, cognition-speech-language development, attention deficit-hyperactivity disorder and autism (6-10).

We evaluated babies with hyperbilirubinaemia using the DDST. In our study, when we compared the patients with hyperbilirubinemia with the control group, we found that their neurodevelopment was significantly retarded (p<0.001). The literature suggests that there is a significant relationship between neonatal hyperbilirubinemia and neurodevelopmental delay, but this relationship seems quite complicated. In a recent study, the factors affecting neurodevelopmental delay in preterm and term babies were examined. In preterm infants, the most important risk factors were intensive care period, ototoxic drug use, mechanical ventilation and hyperbilirubinemia, while in term infants, the risk factors were hyperbilirubinemia and Apgar score (11,12). Another study in term babies found that the higher the bilirubin level, the more negatively the development was affected (13).

Preterm infants are more sensitive to hyperbilirubinaemia. Therefore, the relationship between hyperbilirubinaemia and developmental retardation has been studied mostly in preterm infants. In the many studies conducted in this group, the effect of hyperbilirubinaemia on developmental delay has been found to be quite pronounced (14-17).

As the bilirubin level in the blood increases, newborns are more affected by its possible toxic effects. In our study, newborns with a total bilirubin level greater than 23.5 mg/dL were found to be more at risk in terms of neurodevelopmental delay. In a study with the Baroda developmental screening test, they found that neurodevelopment delay was more likely in term babies with a total bilirubin level greater than 22 mg/dL (13).

DDST is a very reliable and widely used test in evaluating the neurodevelopment of children aged 0-6 years. It has been used to evaluate neurodevelopment in different case groups such as adenotonsillar hypertrophy, congenital heart disease and babies from pre-eclamptic mothers (18-20).

In our study, there was a marked delay in language development in the hyperbilirubinaemia group (p<0.001). In many studies, the effect of hyperbilirubinemia on neurodevelopment has been investigated, but only the impact on hearing has been revealed. None of these studies focused on the relationship between speech delay and hyperbilirubinaemia. There is limited information in the literature about the effect of hyperbilirubinaemia on hearing and language development (18,19,21).

In our study, a statistically significant fine motor developmental delay was found in the hyperbilirubinaemia group compared to the control group (p<0.046). The link between motor retardation and dyskinetic cerebral palsy is well known in newborns exposed to high bilirubin toxicity. However, the effect of exposure to low-moderate bilirubin levels on motor development is not fully understood. More research is needed to understand motor disorders that can be caused by neonatal hyperbilirubinaemia. Movement disorders and cerebral palsy may also develop in preterm babies exposed to low-to-moderate bilirubin levels (22,23).

There was no significant difference in personal-social and gross motor development between the two groups in our study.

Factors such as the paternal and maternal level of education level and the income level of the family can play an important role in the child’s development. In a large-scale study, maternal education has been shown to have a significant effect on the language and fine motor development of preschool children. It was also found that the mother was more effective than the father in impacting the development of the child in early childhood (24-26). In our study, no difference was found between the two groups in terms of the level of education of the parents, the income level of the family and the number of children in the family.

The fact that our study was conducted with a small number of cases can be considered as a limitation. However, the exclusion criteria have been expanded to obtain more accurate results. It is also an advantage that the same person evaluated all children, and the study was done prospectively.

Conclusion

In children without significant developmental disorders, cases of mild neurological damage may not be detected by normal physical examination. In children treated for significant hyperbilirubinaemia, developmental screening tests should be performed at regular intervals, in addition to the detailed systemic examination and hearing testing. Early detection of developmental delays in children is essential for initiating the right treatment in a timely manner.

Ethics

Ethics Committee Approval: This prospective and comparative study was approved by the local ethics committee (approval number: GOKAEK/2017-550, date: 08.02.2017).

Informed Consent: Informed consent was obtained from all patients.

Peer-review: Externally peer-reviewed.

Authorship Contributions: Concept - G.Ö., S.C.; Design - G.Ö., S.C.; Data Collection or Processing - G.Ö.; Analysis or Interpretation - G.Ö., S.C.; Literature Search - G.Ö.; Writing - G.Ö.

Conflict of Interest: No conflict of interest was declared by the authors.

Financial Disclosure: The authors declared that this study received no financial support.