Table 1.

Demographic, gestational, and parental characteristics of population cases and controls, 1968–2016.

Characteristic	Cases (N=5078)		Controls (N=123,228)
	N	%	N	%
Child’s sex
Male	2751	54.2	66,764	54.2
Female	2327	45.8	56,464	45.8
Child’s birthplace
Urban	1702	33.5	40,664	33.0
Rural/Small towns	3376	66.5	82,564	67.0 67.0
Maternal age (years)
≤ 25	1677	33.0	42,188	34.2
26–30	1911	37.6	45,426	36.9
31–35	1077	21.2	26,453	21.5
≥ 36	413	8.1	9161	7.4
Paternal age (years)
≤ 25	908	18.0	23,703	19.3
26–30	1838	36.4	42,816	34.9
31–35	1360	27.0	33,811	27.6
≥ 36	941	18.6	22,391	18.3
Missing (father unknown)	31		507
Family socioeconomic statusa
High	490	12.6	12,063	12.7
Medium-high	681	17.5	15,928	16.8
Medium	718	18.4	17,784	18.7
Medium-low	1266	32.5	31,050	32.7
Low	750	19.0	18,079	19.1
Missing	1183		28,324
Parity
0	2207	43.5	53,553	43.5
1	1910	37.6	46,394	37.6
2+	961	18.9	23,281	18.9
Data available for births 1991+
Maternal smoking status
Smoker	515	23.6	12,339	23.1
Non-smoker	1669	76.4	41,080	76.9
Missing	110		2495

^aMissing data on family socioeconomic status increased over time due to changes in Danish tax law