Research Article: Low gestational age at birth and difficulties in school—A matter of ‘dose’

Date Published: June 20, 2018

Publisher: Public Library of Science

Author(s): Rikke Wiingreen, Gorm Greisen, Jannet Svensson, Bo Mølholm Hansen, Serena Counsell.

http://doi.org/10.1371/journal.pone.0198482

Abstract

Several studies suggest a relationship between gestational age at birth and risk of school difficulties. Our study aimed to investigate the association between the entire range of gestational ages and significant school difficulties measured as 1) More than nine hours per week special educational support and 2) Failing to complete compulsory school.

A population-based register study including all children attending the Danish compulsory school in 2015/2016 and all live-born infants born in Denmark from 1992 to 1997. Data were collected and linked using multiple registers held by Statistic Denmark. Multiple logistic regression analyses were used to estimate the association between gestational age and significant school difficulties, adjusted for explanatory variables.

For measurement 1) “Special educational support” 615,789 children entered the analyses after exclusion of those with missing neonatal data. The risk of special educational support increased gradually across the entire range of gestation from 40 to ≤24 weeks: The adjusted odds ratio was 1.07 (95% confidence interval 1.03–1.12) at 39 weeks of gestational and 6.18 (95% confidence interval 5.17–7.39) at gestational ages < 28 weeks. For measurement 2) “Failing to complete compulsory school” the cohort consisted of 374,798 children after exclusion of those who died, had emigrated and/or had missing neonatal data. The risk of failing to complete compulsory school increased across the entire range of gestational ages: The adjusted odds ratio was 1.07 (95% confidence interval 1.04–1.10) at 39 weeks of gestation and 2.99 (95% confidence interval 2.41–3.71) at gestational ages < 28 weeks. In both sets of analyses GA = 40 weeks was used as reference. We confirm a clear association between the degree of prematurity and significant school difficulties across the entire range of gestational ages from ≤ 24 to 40 weeks.

Partial Text

Preterm born children have increased risk of neurodevelopmental impairments such as cerebral palsy and severe learning disabilities appearing in the first years of life. At school age, school difficulties and academic underachievement have been extensively reported among very preterm born children (gestational age (GA) < 32 weeks) [1–3]. Further, a growing number of studies find that even children born moderate and late preterm also appear having significant school difficulties with lower cognitive abilities compared with their term born peers [4–7]. Thus, there is evidence of a stepwise increase in learning difficulties with decreasing GA rather than a threshold effect concerning the association between learning difficulties and prematurity. However, the majority of previous studies have only examined schooling among different groups of preterm born children and not across the entire range of GA’s as a continuum and the few studies that have investigated the relation as a continuum have almost exclusively investigated intelligence scores (intelligence quotients, IQ) as a proxy for school difficulties and later academic disadvantages [8–11]. However, the consequences for school performance is, still less clear. For the analyses concerning special educational support there were 695,439 children registered as pupils in the compulsory schools in Denmark in the school year 2015/2016. After exclusion of children with missing neonatal-data (n = 39,086, 5.6%) and children who were only registered in 10th grade (n = 40,564, 5.8%), 88.6% (n = 615,789) of all children in compulsory school in Denmark in the school year 2015/2016 were included in the analyses (Fig 1A). In the study population 5.5% (n = 33,786) were born preterm (GA<37 weeks) and 3.5% (n = 21,762) received comprehensive special educational support more than 9 hours weekly. For the analyses concerning “failing to complete compulsory school” 409,902 live born children were registered between 1992 and 1997 in the Medical Birth register. After exclusion of the deceased (n = 2,954, 0.7%), the emigrated (n = 19,471, 4.8%) and those with missing neonatal-data (n = 12,679, 3.1%), 91.4% of children (n = 374,798) born in Denmark in the period 1992–1997 were included in the analyses (Fig 1B). The GA distribution of the emigrated children was almost identical with the GA distribution in the rest of the cohort. In the study population 5.5% (n = 20,596) were born preterm (GA<37 weeks) and a total of 10.3% (n = 38,478) failed to complete compulsory school. In our large population-based study we found that ex-preterm children have an increased risk of school difficulties measured as special educational support and failing to complete compulsory school. Further the association between significant school difficulties and GA increased with decreasing GA from 41 to 24 weeks of gestation including the GA’s classified as “term” (GA 37–41). We investigated the two outcome-measures of school difficulties by two different study-populations and were therefore not able to investigate the specific interaction between the need for special educational and lack of completion of compulsory school. Despite this, the results regarding the two outcomes were very similar with both outcomes showing signs of a similar dose-effect like relationship. Our study therefore indicates that an increased risk of special educational support, not only is a marker of temporary school difficulties since a related association was found for failing to complete compulsory school. These are important outcomes of practical importance. Special education at a level of 9 hours or more weekly is costly, and failing to complete compulsory school has direct implications for further educational possibilities since it predicts a lower chance of receiving further secondary education and thereby predicts a lower final educational level [16]. This is in accordance with a previous study from Denmark comparing 1,422 individuals born at GA<33 weeks with nearly 200,000 term born individuals at age 27–29 years [24]. The rate of individuals with only compulsory school as the final education level was 8% higher in the preterm group and the rate of academic education was 5.7% lower. We confirm a clear association between the degree of prematurity and significant school difficulties across the entire range of GA’s. At the community level, the late preterm and early term born infants who failed to complete compulsory school after 10 years of education far outnumber the very preterm born infants.   Source: http://doi.org/10.1371/journal.pone.0198482

 

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