Table 2.

Association between conditional variables and neurodevelopmental delay at six months old in boys

Conditional variables at birth and 4 months old	Total	Communication	Gross motor	Fine motor	Problem solving	Personal-Social
	2,714/31,399 (8.6 %)	578/31,595 (1.8 %)	526/31,590 (1.7 %)	823/31,506 (2.6 %)	1,204/31,590 (3.8 %)	492/31,539 (1.6 %)
Length at birth	0.99 (0.95–1.04)	0.93 (0.83–1.03)	0.90 (0.80-1.00)	1.01 (0.92–1.10)	1.01 (0.94–1.09)	1.02 (0.91–1.15)
Weight at birth	0.91 (0.87–0.96)	1.02 (0.92–1.14)	0.97 (0.86–1.08)	0.88 (0.80–0.96)	0.88 (0.82–0.95)	0.87 (0.77–0.98)
cLength at 4 months old	0.85 (0.82–0.88)	0.84 (0.76–0.92)	0.83 (0.77–0.90)	0.82 (0.77–0.88)	0.84 (0.79–0.90)	0.84 (0.77–0.92)
crWeight at 4 months old	1.03 (0.98–1.08)	0.88 (0.79–0.99)	1.24 (1.11–1.38)	0.99 (0.90–1.09)	0.98 (0.90–1.06)	1.11 (0.98–1.25)

Data represent the adjusted relative risk (95 % confidence interval). All of the conditional variables and the following covariates were included together in the model: maternal age and smoking, maternal and paternal education, family income, and home speech stimulation.

cLength conditional length; crWeight conditional relative weight