title: Maternal use of folic acid supplements and infant risk of neural tube defects in Norway 1999-2013.
abstract: OBJECTIVE
  Like most European countries, Norway has refrained from mandatory food fortification with folic acid to reduce the number of neural tube defects. We explored the role of folic acid and multivitamin supplements in the prevention of neural tube defects among newborn infants.
  
  
  METHODS
  We used data from the Medical Birth Registry of Norway, 1999-2013. A total of 528,220 women had 880,568 pregnancies resulting in 896,674 live- and stillborn infants, of whom 270 had neural tube defects. Relative risks were estimated with log-binomial regression.
  
  
  RESULTS
  From 1999 to 2013, intake of folic acid supplements increased from 4.8% to 27.4%. Vitamin supplement use was more frequent in older, married or cohabiting women and those with lower parity, as well as women who did not smoke during pregnancy. The overall adjusted relative risk of infant neural tube defects associated with maternal vitamin intake before pregnancy relative to no intake was 0.76 (95% confidence interval: 0.53-1.10). When we divided our study period in two (1999-2005 and 2006-2013), we found a significantly reduced risk of neural tube defects overall by vitamin use in the second time period, but not in the first: adjusted relative risk 0.54 (95% confidence interval: 0.31-0.91) and 1.02 (95% confidence interval: 0.63-1.65), respectively.
  
  
  CONCLUSIONS
  OVER THE FULL STUDY PERIOD, WE FOUND NO STATISTICALLY SIGNIFICANT ASSOCIATION BETWEEN VITAMIN USE AND NEURAL TUBE DEFECTS OVERALL HOWEVER, VITAMIN USE WAS ASSOCIATED WITH A SIGNIFICANTLY LOWER RISK OF NEURAL TUBE DEFECTS IN THE SECOND HALF OF THE STUDY PERIOD, 2006-2013.
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Norway Department of Dermatology, Haukeland University Hospital, Norway trude.gildestad@uib.no.
authors.forename: Trude
authors.initials: T
authors.lastname: Gildestad
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Norway Center for Medical Genetics and Molecular Medicine, Haukeland University Hospital, Norway.
authors.forename: Nina
authors.initials: N
authors.lastname: Øyen
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Norway Medical Birth Registry of Norway, Norwegian Institute of Public Health, Norway.
authors.forename: Kari
authors.initials: K
authors.lastname: Klungsøyr
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Norway Centre for Clinical Research, Haukeland University Hospital, Norway.
authors.forename: Roy Miodini
authors.initials: RM
authors.lastname: Nilsen
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Norway Medical Birth Registry of Norway, Norwegian Institute of Public Health, Norway.
authors.forename: Anne Kjersti
authors.initials: AK
authors.lastname: Daltveit
authors.affiliation: Department of Global Public Health and Primary Care, University of Bergen, Norway Centre for Disease Burden; Norwegian Institute of Public Health, Norway.
authors.forename: Stein Emil
authors.initials: SE
authors.lastname: Vollset
mesh_terms: D019587:Dietary Supplements / Q000706:statistics & numerical data*; D005260:Female; D005492:Folic Acid / Q000008:administration & dosage*; D006801:Humans; D007231:Infant, Newborn; D009436:Neural Tube Defects / Q000453:epidemiology*; D009664:Norway / Q000453:epidemiology; D011247:Pregnancy; D012042:Registries; D012306:Risk
chemical_list: D005492:Folic Acid
keywords: Neural tube defects; Norway; epidemiology; folate; folic acid; health promotion; multivitamins; reproduction