Table 2. Perinatal characteristics and childhood leukaemia.

	ALL				AML
	Cases (N=408)	Controls (N=567)	ORa	95% CI	Cases (N=65)	Controls (N=567)	ORa	95% CI
Mean birth weight (g)
Mean	3322	3314			3294	3314
s.d.b	(514)	(522)			(396)	(522)
Birth weight (g)
<2500	22	31	1.0	(0.6–1.9)	1	31	0.3	(0.03–2.1)
2500–2999	73	96	1.1	(0.7–1.6)	12	96	0.9	(0.4–1.9)
3000–3499	160	217	1.0	Ref	32	217	1.0	Ref
3500–3999	97	172	0.8	(0.6–1.1)	14	172	0.6	(0.3–1.2)
⩾4000	40	37	1.4	(0.8–2.3)	3	37	0.8	(0.2–2.8)
Xc	16	14			3	14
Term of pregnancy
<37	41	45	1.4	(0.9–2.2)	5	45	1.4	(0.5–4.1)
37–38	80	144	0.7	(0.5–1.0)	13	144	1.0	(0.5–2.1)
39–40	220	304	1.0	Ref	32	304	1.0	Ref
⩾41	32	52	0.9	(0.5–1.5)	7	52	1.3	(0.5–3.3)
Xc	35	22			8	22
Birth order
1	180	267	1.0	Ref	35	267	1.0	Ref
2	131	199	0.9	(0.7–1.2)	12	199	0.5	(0.2–1.0)
3	64	73	1.1	(0.8–1.7)	12	73	1.3	(0.6–2.8)
4+	32	22	2.0	(1.1–3.7)	5	22	2.5	(0.8–7.5)
Xc	1	6			1	6
	P-trend =0.07				P-trend>0.10
Maternal age at birth
<25	84	93	1.4	(1.0–2.1)	11	93	0.9	(0.4–2.0)
25–29	154	241	1.0	Ref	30	241	1.0	Ref
30–34	107	169	0.9	(0.7–1.3)	14	169	0.7	(0.3–1.3)
⩾35	57	56	1.6	(1.0–2.5)	8	56	1.3	(0.5–3.1)
Xc	6	8			2	8
Previous foetal losses
0	313	436	1.0	Ref	49	436	1.0	Ref
1	74	88	1.2	(0.8–1.7)	11	88	1.1	(0.5–2.3)
⩾2	16	28	0.8	(0.4–1.6)	2	28	0.6	(0.1–2.8)
Xc	5	15			3	15
Down's syndrome
No	400	565	1.0	Ref	63	565	1.0	Ref
Yes	8	2	4.4	(0.9–2.2)	2	2	11.7	(1.3–108.5)

^aAdjusted for stratification variables (gender, age at diagnosis, region of residence at diagnosis).

^bs.d.=standard deviation.

^cX=missing values.