Table 1.

Characteristics of the mother and pregnancy associated with the risk of hospital admission for bronchiolitis in infancy

	Number of children with bronchiolitis (total number with each characteristic)	% with bronchiolitis	p Value	Adjustment for year of birth, social class, mother’s age, parity, smoking and sex: OR (95% CI)
Year of birth
1970–1974	397 (69 372)	0.57	<0.001
1975–1979	273 (56 768)	0.48
1980–1984	530 (60 446)	0.88
1985–1989	887 (57 122)	1.55
Total	2087 (243 708)	0.86
Mother's age (years)
14–19	260 (17 611)	1.48	<0.001	2.36 (1.81 to 3.08)
20–24	729 (67 447)	1.08		1.42 (1.22 to 1.66)
25–29	648 (90 467)	0.72		1 (1)
30–34	325 (49 544)	0.66		0.87 (0.73 to 1.03)
35–39	106 (15 423)	0.69		0.63 (0.48 to 0.84)
40+	18 (2896)	0.62		0.70 (0.39 to 1.26)
Total	2086 (243 388)	0.86
Social class
1 (high)	88 (22 368)	0.39	<0.001	1 (1)
2	289 (46 092)	0.63		1.49 (1.12 to 1.99)
3	723 (87 431)	0.83		1.81 (1.38 to 2.38)
4	286 (25 999)	1.10		2.20 (1.64 to 2.97)
5 (low)	152 (9776)	1.55		2.34 (1.65 to 3.30)
Total	1538 (191 666)	0.80
Married
Yes	1675 (220 269)	0.76	<0.001	1 (1)
No	411 (22 996)	1.79		1.13 (0.92 to 1.38)
Total	2086 (243 265)	0.86
Cigarettes smoked per day
None	822 (103 596)	0.79	<0.001	1 (1)
1–4	42 (3765)	1.12		1.23 (0.84 to 1.80)
5–14	250 (13 668)	1.83		1.89 (1.59 to 2.25)
15+	298 (12 991)	2.29		2.09 (1.77 to 2.48)
Total	1412 (134 020)	1.05
Parity
1	806 (87 340)	0.92		1.93 (1.65 to 2.25)
2	387 (35 342)	1.10		2.26 (1.87 to 2.73)
3+	256 (18 387)	1.39		2.73 (2.17 to 3.43)
Total	2083 (243 159)	0.86
Pre-eclampsia
No	1917 (219 636)	0.70	0.006	1 (1)
Yes	168 (24 023)	0.87		1.20 (0.96 to 1.50)
Total	2085 (243 659)	0.86

Data from the Oxford Record Linkage Study specialist maternity dataset.