Table 5. Risk of Acute Lymphoblastic Leukemia Associated with Use of Vitamin and Folic Acid Supplementation Before and by Trimester During Pregnancy: Subsets of Childhood Leukemia International Consortium Studies.

Use Before and During Pregnancy	Vitamins (7 Studies)a				Folic Acid (5 Studies)b
	No. Controls (n=6098)	No. Cases (n=4020)	OR	(95% CI)c	No. Controls (n=3608)	No. Cases(n=1898)	OR	(95% CI)c
Nod	2235	1183	1.00		2326	1096	1.00
Yes	3863	2837	0.78	(0.69–0.88)	1282	802	0.78	(0.67–0.91)
Preconception only	41	29	0.85	(0.51–1.39)	21	12	1.05	(0.51–2.18)
Trimester 1e	288	151	0.79	(0.63–0.99)	268	132	0.80	(0.63–1.03)
Trimester 2/3e	445	330	0.86	(0.72–1.03)	270	145	0.66	(0.52–0.84)
Trimester 1/2/3e	3089	2327	0.75	(0.66–0.85)	723	513	0.82	(0.69–0.98)

^aStudies include: Australia, Brazil, Canada, Egypt, France, US CCG, US NCCLS (2003–2008)

^bStudies include: Australia, Brazil, Canada, France, US NCCLS (2003–2008)

^cPooled OR adjusted for age, sex, ethnicity, parental education, and study

^dReference category

^eMay or may not include preconception use