title: Systematic review of first-trimester vitamin D normative levels and outcomes of pregnancy.
abstract: OBJECTIVE
  We undertook a systematic review to assess normative levels of vitamin D in early pregnancy and association with subsequent pregnancy outcomes.
  
  
  METHODS
  Medline and Embase databases and reference lists were searched. Inclusion criteria were pregnant populations, blood sample taken during the first trimester, and serum hydroxyvitamin D levels assessed.
  
  
  RESULTS
  Eighteen studies reported vitamin D levels in first trimester (n = 11-3730), and 5 examined pregnancy outcomes. Mean vitamin D concentrations differed when stratified by ethnicity: white (mean [SD]: 29.4 [11.7] to 73.1 [27.1] nmol/L) and nonwhite (15.2 [12.1] to 43 [12] nmol/L). Most studies used general population cut points to define deficiency and found a large proportion of women deficient. Two articles examined risk of preeclampsia and reported differing findings, whereas 2 of 3 found low levels associated with increased risk of small-for-gestational age births.
  
  
  CONCLUSIONS
  There is no clear definition of vitamin D deficiency in pregnancy and insufficient evidence to suggest low vitamin D levels in early pregnancy are associated with adverse pregnancy outcomes.
authors.affiliation: Kolling Institute of Medical Research, University of Sydney, NSW, Australia. natasha.nassar@sydney.edu.au
authors.forename: Natasha
authors.initials: N
authors.lastname: Nassar
authors.forename: Genevieve H
authors.initials: GH
authors.lastname: Halligan
authors.forename: Christine L
authors.initials: CL
authors.lastname: Roberts
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Morris
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Ashton
mesh_terms: D005260:Female; D006801:Humans; D011225:Pre-Eclampsia / Q000097:blood; D011247:Pregnancy; D011256:Pregnancy Outcome; D011261:Pregnancy Trimester, First / Q000097:blood*; D012016:Reference Values; D012307:Risk Factors; D014807:Vitamin D / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood
chemical_list: D014807:Vitamin D