Table 3. Hazard ratios (HRs) with 95% confidence intervals (95% CI) of childhood cancer by perigestational supplementation of folic acid and/or multivitamins, among 687 406 children, Norway, 1999–2010.

Cancer types	Supplementsa	Cancer cases	HRb	95% CI	PTrend
All cancers	No supplements	424	1.00	Reference
	Multivitamins only	61	1.05	0.78–1.42
	Folic acid only	154	1.13	0.92–1.38
	Folic acid and multivitamins	160	1.02	0.83–1.25	0.60
I Leukemias, myeloproliferative diseases, and myelodysplastic diseases
	No supplements	135	1.00	Reference
	Multivitamins only	21	1.23	0.75–2.01
	Folic acid only	50	1.13	0.79–1.63
	Folic acid and multivitamins	62	1.25	0.89–1.76	0.20
(a) Lymphoid leukemia
	No supplements	100	1.00	Reference
	Multivitamins only	16	1.30	0.75–2.27
	Folic acid only	42	1.30	0.87–1.95
	Folic acid and multivitamins	50	1.31	0.89–1.94	0.12
(b) Acute myeloid leukemia
	No supplements	28	1.00	Reference
	Multivitamins only	3	0.97	0.29–3.27
	Folic acid only	5	0.59	0.22–1.60
	Folic acid and multivitamins	9	0.96	0.43–2.17	0.67
II Lymphomas and reticuloendothelial neoplasms
	No supplements	25	1.00	Reference
	Multivitamins only	3	0.55	0.13–2.33
	Folic acid only	5	0.40	0.12–1.34
	Folic acid and multivitamins	9	0.96	0.42–2.21	0.51
III CNS and miscellaneous intracranial and intraspinal neoplasms
	No supplements	107	1.00	Reference
	Multivitamins only	14	1.08	0.60–1.94
	Folic acid only	37	1.18	0.78–1.78
	Folic acid and multivitamins	27	0.68	0.42–1.10	0.32
(b) Astrocytoma
	No supplements	44	1.00	Reference
	Multivitamins only	8	1.57	0.72–3.40
	Folic acid only	15	1.31	0.70–2.45
	Folic acid and multivitamins	12	0.86	0.43–1.73	0.97
(c) Intracranial and intraspinal embryonal tumours
	No supplements	28	1.00	Reference
	Multivitamins only	2	0.61	0.14–2.59
	Folic acid only	12	1.28	0.60–2.76
	Folic acid and multivitamins	8	0.69	0.27–1.74	0.69
IV Neuroblastoma and other peripheral nervous cell tumours
(a) Neuroblastoma and ganglioneuroblastoma
	No supplements	37	1.00	Reference
	Multivitamins only	5	0.99	0.35–2.82
	Folic acid only	15	1.08	0.54–2.15
	Folic acid and multivitamins	14	1.05	0.53–2.06	0.85
VI Renal tumours
(a) Wilms' tumour
	No supplements	28	1.00	Reference
	Multivitamins only	5	1.60	0.60–4.25
	Folic acid only	9	1.01	0.42–2.40
	Folic acid and multivitamins	10	1.16	0.52–2.58	0.76
IX Soft tissue and other extraosseous sarcomas
	No supplements	32	1.00	Reference
	Multivitamins only	5	1.12	0.39–3.22
	Folic acid only	18	1.72	0.90–3.29
	Folic acid and multivitamins	9	0.77	0.34–1.75	0.90

Abbreviation: CNS=central nervous system.

^aMaternal supplement intake before and/or during pregnancy, categorised by folic acid content: No use; multivitamins (approximately 0.2 mg); folic acid supplements (0.4 mg); and folic acid and multivitamins (approximately 0.6 mg).

^bHazard ratios (HR) with 95% confidence intervals (95% CI) adjusted for birth order (1, 2, ⩾3), smoking (never, sometimes, ⩽10 cigarettes daily, >10 cigarettes daily, daily smoking of unknown amount), maternal and paternal age (<25, 25–34, ⩾35 years), and maternal and paternal education (compulsory, intermediate, tertiary) comparing cancer risk in children exposed to periconceptional folic acid (multivitamins, folic acid, folic acid and multivitamins) and cancer risk in children without perigestational folic acid exposure (reference).