Table 2. Association between parental occupational exposures and childhood acute leukemia during four periods of exposure. a: odds ratio, b: confidence interval.

Occupational exposure groups	Cases (N=108)		Controls (N=108)		Crude ORa [95% CIb]
	N	%	N	%
High contact level
Maternal exposure
1 year before conception	53	49.1	53	49.1	0.95 [0.53-1.71]
During pregnancy	37	34.3	34	31.5	1.00 [0.53-1.90]
During breastfeeding	12	11.1	5	4.6	2.04 [0.61-6.79]
From child’s birth until diagnosis	53	49.1	44	40.7	1.46 [0.80-2.65]
Paternal exposure
1 year before conception	33	30.6	33	30.6	1.00 [0.53-1.88]
During pregnancy	32	29.6	34	31.5	0.93 [0.50-1.75]
During breastfeeding	32	29.6	33	30.6	0.97 [0.51-1.81]
From child’s birth until diagnosis	37	34.3	38	35.2	0.93 [0.50-1.72]
Chemicals
Maternal exposure
1 year before conception	21	19.4	24	22.2	0.73 [0.36-1.52]
During pregnancy	14	13.0	12	11.1	1.14 [0.47-2.78]
During breastfeeding	3	2.8	5	4.6	0.36 [0.07-2.04]
From child’s birth until diagnosis	22	20.4	20	18.5	1.02 [0.47-2.21]
Paternal exposure
1 year before conception	66	61.1	66	61.1	0.88 [0.48-1.60]
During pregnancy	67	62.0	67	62.0	0.88 [0.48-1.60]
During breastfeeding	67	62.0	65	60.2	0.94 [0.52-1.71]
From child’s birth until diagnosis	65	60.2	69	63.9	0.78 [0.43-1.44]
Electromagnetic fields
Paternal exposure
1 year before conception	6	5.6	6	5.6	1.49 [0.42-5.35]
During pregnancy	6	5.6	6	5.6	1.49 [0.42-5.35]
During breastfeeding	6	5.6	6	5.6	1.49 [0.42-5.35]
From child’s birth until diagnosis	6	5.6	6	5.6	1.58 [0.45-5.46]