Samples and immunoassays
Maternal serum samples were collected after the occurrence of hypertension from the surplus aliquots of routine biochemical assay at any point between 20+0 and 36+6 weeks. The concentrations of sFlt-1 and PlGF were measured by an automated immunoassay platform (Cobas e411 module, Roche Diagnostic) in the central laboratory of our hospital according to the protocol provided by the manufacturer. Intra- and inter-coefficient variance was below 2.0% and 4.0%, respectively. Ratio of sFlt-1 to PlGF was calculated for each sample.