Maternal Biomarkers in Pregnancy

In the first trimester (median 13.2, 95% range 9.6, 7.6 weeks) and second trimester (median 20.4, 95% range 18.5, 23.5 weeks) maternal venous blood plasma samples were drawn [19 (link)–21 (link)]. Blood samples were centrifuged and thereafter stored at –80 °C. sFlt-1 and PlGF concentrations were analyzed using a prototype of a microparticle-enhanced immunoassay on the Architect System (Abbott Diagnostics B.V., Hoofddorp, the Netherlands). The between-run coefficients of variation for plasma sFlt-1 were 2.8% at 5.5 ng/mL and 2.3% at 34.0 ng/mL; and 4.7% at 24 pg/mL, and 3.8% at 113 pg/mL for plasma PlGF. The highest detected level was 150 ng/mL for sFlt-1 and 1500 pg/mL for PlGF [21 (link)]. The sFlt-1/PlGF ratio was calculated by dividing the sFlt-1 concentration by the PlGF concentration. Because these measurements were not normally distributed, we log-transformed them for further analyses. Maternal PlGF and sFlt-1 concentrations and sFlt-1/PlGF ratio were categorized as quintiles and analyzed across the full range after construction of standard deviation (SDS) scores.