Table.

Risk of childhood leukaemia in relation to ultrasound examinations and number of examinations: results of Swedish population based nationwide case-control study

	Myeloid leukaemia				Lymphatic leukaemia
	No of cases	No of controls	Odds ratio* (95% CI)		No of cases	No of controls	Odds ratio* (95% CI)
All pregnancies
Not exposed to ultrasound	334	318	1.00		42	39	1.00
Exposed	200	214	0.85 (0.62 to 1.16)		29	27	1.00 (0.42 to 2.40)
Missing information†	44	46	NA		3	8	NA
No of ultrasound examinations
None	334	318	1.00		42	39	1.00
1 or 2	161	159	0.93 (0.67 to 1.23)		22	20	1.00 (0.40 to 2.50)
⩾3	39	55	0.64 (0.40 to 1.04)		7	7	1.00 (0.30 to 3.33)
Missing information†	44	46	NA		3	8	NA
Odds ratio (linear trend)‡	NA	NA	0.95 (0.85 to 1.06)		NA	NA	1.01 (0.74 to 1.38)

NA=Not applicable. ^*Calculated by means of conditional logistic regression. ^†Missing information on exposure. 

^‡Calculated by means of conditional logistic regression, assuming linear effect for number of ultrasound examinations.