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

Abstract

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