Elevated risk of attention deficit hyperactivity disorder (ADHD) in Japanese children with higher genetic susceptibility to ADHD with a birth weight under 2000 g

Table 2 Association of birth weight categories with ADHD scores among Japanese children at age 8–9 years (N=796)

Birth weight	Rate ratio (95% confidence intervals)
Birth weight	ADHD total score	Inattention score	Hyperactivity score
Model 1^†
Normal birth weight (ref.)	1.00	1.00	1.00
Birth weight 2000–2499 g	0.88 (0.68–1.13)	0.90 (0.70–1.15)	0.83 (0.60–1.15)
Birth weight < 2000 g	1.60 (1.16–2.22)**	1.50 (1.10–2.06)*	1.82 (1.17–2.83)**
Model 2^‡
Normal birth weight (ref.)	1.00
Birth weight 2000–2499 g	1.00 (0.77–1.30)	1.00 (0.77–1.29)	0.99 (0.70–1.40)
Birth weight < 2000 g	1.60 (1.21–2.12)**	1.51 (1.17–1.95)**	1.85 (1.23–2.77)**
Model 3^§
Normal birth weight (ref.)	1.00
Birth weight 2000–2499 g	1.00 (0.77–1.29)	1.00 (0.77–1.29)	0.99 (0.71–1.39)
Birth weight < 2000 g	1.57 (1.19–2.09)**	1.49 (1.15–1.94)**	1.78 (1.19–2.67)**

Note: Normal birth weight was defined as birth weight ≥ 2500 g; ref., reference category; values in bold show statistical significance; **p<0.01; *p<0.05
^†Model 1 was adjusted for variations in survey time only
^‡Model 2 additionally adjusted for gender of child, parity, maternal age, education, pre-pregnancy body mass index, pre-pregnancy smoking status, and alcohol intake
^§Model 3 additionally adjusted for father’s age at birth and household annual income

ISSN: 1741-7015