Samples collection and angiogenic factors measurement
At admission and before delivery (within 12 hours), a 5 ml peripheral maternal blood sample was obtained. Serum was separated by centrifugation at 2000 g for 10 min at room temperature, and samples were immediately stored at -80ÂșC until assayed at an independent laboratory.
Maternal serum concentrations of sFlt-1 and PlGF were determined by the fully automated Elecsys assays for sFlt-1 and PlGF on an electrochemiluminescence immunoassay platform (Cobas analyzers, Roche Diagnostics). In all the kits, the intra-assay precision was <4% for both assays and the inter-assay precision was 2.3-5.6% and 2.4-4.6% for sFlt-1 and PlGF assays respectively.
Longitudinal changes were quantified by calculating delta values: (level at delivery - levels at admission)/days from admission to delivery.