Internalising and externalising behaviour in siblings of children born preterm Preterm birth: Internalising and externalising behaviour of siblings

The family environment in which children grow up is associated with the development of their behaviour. It has been proposed that changes in family dynamics, associated with a child being born preterm, can influence siblings' health. We tested the hypothesis that term-born children (≤ 14 years of age) with younger preterm born siblings are at an increased risk of having higher internalising and externalising behaviour problems than term-born children with term-born siblings. We also compared scores with children without siblings. We used harmonised data from four European birth cohorts. We grouped 65,711 term-born children (49% girls) across the four cohorts as follows: risk group (with younger preterm born siblings; n = 427), reference group (with only term siblings; n = 12,371), and only-child group (without siblings; n = 52,913). We investigated whether the internalising and externalising z-standardised scores of the term-born children differ by group. The scores came from parent-completed Strengths and Difficulties Questionnaire or Child Behaviour Checklist. Scores of the risk and only-child groups were compared to the reference group. Analyses were conducted in three age groups: ≤ 4, 5-10 and 11-14 years of age. We conducted a two-stage individual participant data meta-analysis and found no evidence of differences in internalising or externalising scores between the risk and the reference groups within any of the age groups. In contrast, the internalising and externalising scores of the only-child participants were higher than the reference group (Internalising- ≤ 4 years: mean difference (MD)=0.06 [95%CI = 0.03,0.08]; 5-10 years: MD = 0.12 [-0.01,0.25]; 11-14 years: MD = 0.07 [0.03,0.12]; Externalising- ≤ 4 years: MD = 0.06 [0.03,0.08]; 5-10 years: MD = 0.10 [0.06,0.15]; 11-14 years: MD = 0.09 [-0.03,0.21]).We found no evidence supporting that having a younger sibling born preterm is a risk factor for increased internalising or externalising behaviour. However, we observed higher internalising and externalising scores in children without siblings compared to those with term-born siblings.