Table 2.

Birth weight for gestational age percentiles and gestational age and risk of intellectual disability in non-malformed, term or post-term, appropriate-for-gestational-age children (complete case analysis) (N = 721,094)

Characteristics	Any intellectual disability
	Population analysis			Sibling comparison analysis
	No. of children	No. of cases	HR (95%CI)	No. of children	No. of cases	HR (95%CI)
Birth weight for gestational age percentiles
Total	721,094	1415		260,928	482
10th–24th	136,786	338	1.43 (1.22–1.67)	43,641	113	1.52 (1.00–2.31)a
25th–39th	141,509	307	1.28 (1.10–1.50)	53,677	120	1.44 (1.00–2.09)b
40th–59th	189,271	318	Ref	69,628	103	Ref
60th–74th	132,855	235	1.04 (0.88–1.23)	52,251	86	1.25 (0.79–1.97)
75th–90th	120,673	217	1.03 (0.87–1.23)	41,731	60	1.25 (0.77–2.02)
Gestational age (weeks)
Total	721,094	1415		245,625	456
37–38	132,997	282	1.18 (1.00–1.39)c	40,987	80	1.33 (0.82–2.16)
39	172,855	340	1.16 (1.00–1.34)d	60,831	113	0.96 (0.65–1.41)
40	217,163	367	Ref	72,671	126	Ref
41	140,970	284	1.17 (1.00–1.36)c	50,216	92	0.79 (0.51–1.24)
≥ 42	57,109	142	1.23 (1.00–1.50)e	20,920	45	1.07 (0.57–2.01)

In population analysis, model was adjusted for maternal age at delivery, parity, educational level, country of birth, smoking during pregnancy, height, BMI in early pregnancy, maternal diabetic and hypertensive diseases, as well as child’s sex, calendar period of delivery, onset of labor, and mode of delivery. In sibling comparison analysis, model was adjusted for maternal age at delivery, parity, smoking during pregnancy, BMI in early pregnancy, maternal diabetic and hypertensive diseases, and child’s sex, calendar period of delivery, onset of labor, and mode of delivery

^aP = 0.050

^bP = 0.053

^cP = 0.054

^dP = 0.041

^eP = 0.049