Systematic review of first-trimester vitamin D normative levels and outcomes of pregnancy

OBJECTIVE: We undertook a systematic review to assess normative levels of vitamin D in early pregnancy and association with subsequent pregnancy outcomes. STUDY DESIGN: 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. CONCLUSION: 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.