| Level I | Good quality evidence |
Systematic review of RCTs with consistent findings High quality individual RCT |
| Level II |
Limited quality patient orientated evidence |
Systematic review of lower quality studies or studies with inconsistent findings Low quality clinical trial Cohort studies Case-control studies |
| Level III | Other |
Consensus guidelines, extrapolations from bench research, usual practice, opinion, disease-oriented evidence (intermediate or physiologic outcomes only), or case series |
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Folic acid, oral: Atta CA, Fiest KM, Frolkis AD, Jette N, Pringsheim T, St Germaine-Smith C, Rajapakse T, Kaplan GG, Metcalfe A. Global Birth Prevalence of Spina Bifida by Folic Acid Fortification Status: A Systematic Review and Meta-Analysis. Am J Public Health. 2016 Jan;106(1):e24-34. https://www.ncbi.nlm.nih.gov/pubmed/26562127
Folic acid, oral: Viswanathan M, Treiman KA, Kish-Doto J, Middleton JC, Coker-SchwimmerEJ, Nicholson WK. Folic Acid Supplementation for the Prevention of Neural Tube Defects: An Updated Evidence Report and Systematic Review for the US Preventive Services Task Force. JAMA. 2017 Jan 10;317(2):190-203. https://www.ncbi.nlm.nih.gov/pubmed/28097361
Folic acid, oral: RCOG. Nutrition in Pregnancy: Scientific Impact Paper No. 18. https://www.rcog.org.uk/en/guidelines
Folic acid, oral: ACOG Committee on Practice Bulletins. ACOG practice bulletin. Clinical management guidelines for obstetrician-gynecologists. Number 44, July 2003. (Replaces Committee Opinion Number 252, March 2001) Obstet. Gynecol. 2003;102(1):203–213. https://www.ncbi.nlm.nih.gov/pubmed/12850637
Folic acid, oral: U.S. Preventive Services Task Force.Folic acid for the prevention of neural tube defects: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2009 May 5;150(9):626-31. https://www.ncbi.nlm.nih.gov/pubmed/19414842
Folic acid, oral: Wilson RD; Genetics Committee, Wilson RD, Audibert F, Brock JA, Carroll J, Cartier L, Gagnon A, Johnson JA, Langlois S, Murphy-Kaulbeck L, Okun N, Pastuck M; Special Contributors, Deb-Rinker P, Dodds L, Leon JA, Lowel HL, Luo W, MacFarlane A, McMillan R, Moore A, Mundle W, O'Connor D, Ray J, Van den Hof M. Pre-conception Folic Acid and Multivitamin Supplementation for the Primary and Secondary Prevention of Neural Tube Defects and Other Folic Acid-Sensitive Congenital Anomalies. J ObstetGynaecol Can. 2015 Jun;37(6):534-52. https://www.ncbi.nlm.nih.gov/pubmed/26334606