Blood sample collection and fatty acid analysis
BLOOD, CLOT
Blood was collected in serum separator tubes from cord blood (2 mL) and infant arterial or venous blood (0.6 mL) at postnatal age (PNA) 1, 3, 7, 14, 28, and 42 days and at postmenstrual age (PMA) 30, 32, 34, 36, and 40 weeks. Blood samples were allowed to clot for a minimum of 0.5 h and a maximum of 2 h before centrifugation (1500 For analysis, serum (25 mL) was spiked with an internal standard (1,2-dinonadecanoyl-sn-glycero-3-phosphocholine), and the sample was lyophilized. Total lipids were extracted [We observed differences between extraction batches in the absolute quantification related to the analyst and the methylation reagent lot. The internal control sample was therefore used to normalize between extraction batches. Adjustments were made for each fatty acid separately, using a ratio between the concentration of the internal control in each batch and the mean concentration of the internal control sample for all batches. The inter-assay CV for the relative quantification of DHA, AA, and LA were 11.9%, 6.9%, and 6.8%, respectively. The inter-assay CV for the absolute quantification of DHA, AA, and LA were 10.2%, 9.2%, and 10.1%, respectively.