Evidence for a causal association of low birth weight and attention problems
Maria M Groen-Blokhuis1, Christel M Middeldorp, Catharina E M van Beijsterveldt
1VU University, Department of Biological Psychology, Van der Boechorststraat 1, 1081 BT Amsterdam, The Netherlands. m.m.groen-blokhuis@vu.nl
Insights
Lower birth weight (BW) causally influences attention problems (AP) in children. Catch-up growth (CUG) in low-BW infants does not explain this association, indicating a direct link between BW and AP development.
Area of Science:
- Developmental Psychology
- Pediatrics
- Genetics
Background:
- Low birth weight (LBW) is linked to attention problems (AP) and attention-deficit/hyperactivity disorder (ADHD).
- The underlying reasons for this association, particularly causality, remain unclear.
- Investigating the role of catch-up growth (CUG) in potentially mediating this relationship is crucial.
Purpose of the Study:
- To determine if birth weight (BW) has a causal effect on attention problems (AP).
- To examine whether catch-up growth (CUG) mediates the relationship between LBW and AP.
- To analyze these relationships using a large twin cohort.
Main Methods:
- Longitudinal analysis of over 29,000 twin pairs from the Netherlands Twin Register.
- Utilized the cotwin control method to account for genetic and environmental factors.
- Assessed hyperactivity and AP at multiple ages (3, 7, 10, 12 years) and weight at birth and 2 years.
Main Results:
- Children with LBW (1,500-2,000 g) exhibited higher AP scores (0.18-0.37 SD) compared to reference BW (3,000-3,500 g).
- This effect was consistent across term and preterm infants.
- Twin analyses (MZ, DZ, UR) revealed that lower BW within pairs predicted higher AP, supporting a causal link.
- Catch-up growth (CUG) did not influence AP scores in LBW twins, ruling out mediation.
Conclusions:
- The association between birth weight and attention problems is strongly indicative of a causal relationship.
- Catch-up growth does not explain the observed effects of low birth weight on attention problems.
Objective:
Low birth weight (LBW) is associated with attention problems (AP) and attention-deficit/hyperactivity disorder (ADHD). The etiology of this association is unclear. We investigate whether there is a causal influence of birth weight (BW) on AP and whether the BW effect is mediated by catch-up growth (CUG) in low-BW children.
Method:
Longitudinal data from >29,000 twins registered with the Netherlands Twin Register with BW ≥1,500 g and gestational age (GA) ≥32 weeks were analyzed with the cotwin control method. Hyperactivity and AP were assessed at ages 3, 7, 10, and 12 years; weight was assessed at birth and age 2 years.
Results:
Children in the lowest BW category of 1,500 to 2,000 g scored 0.18 to 0.37 standard deviations (SD) higher on AP than children in the reference category of 3,000 to 3,500 g. This effect was present in term-born and preterm-born children. Importantly, in BW discordant monozygotic (MZ), dizygotic (DZ), and unrelated (UR) pairs, the child with the lower BW scored higher on hyperactivity and AP than the child with the higher BW and within-pair differences were similar for MZ, DZ, and UR pairs. This pattern is consistent with a causal effect of BW on AP. MZ and DZ twin pairs concordant for LBW but discordant for CUG showed similar AP scores, thus ruling out any effect of CUG on AP.
Conclusions:
These results strongly indicate that the association of birth weight and AP represents a causal relationship. The effects of BW are not explained by CUG in LBW children.
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