Several studies reported the relationship between plasma phytosterol concentrations and parenteral nutrition-associated cholestasis (PNAC). Information on plasma phytosterols half-lives in very-low-birth-weight (VLBW) preterm infants on lipid parenteral nutrition (PN) are lacking. In a prospective cohort study, plasma phytosterols (campesterol, stigmasterol and sitosterol) of VLBW preterm infants on routine PN will be measured by gas chromatography-mass spectrometry (GC-MS) during PN administration and after only lipid stopping. Plasma phytosterols half-lives will be calculated from the monoexponential decay curves. Blood samples will be weekly collected from 1st to 7th week of life during routine metabolic tolerance analysis or gas-analysis in order to avoid burden of additional phlebotomy. Samples will be collected in ethylenediaminetetraacetic acid-tubes and immediately centrifugated. Plasma will be stored in pyrogallol added-tubes at -20°C until analysis. Saponification reaction will be done using 5-alpha-cholestane as internal standard.