**6. Biochemical parameters**

The problem of the Doppler examination alone, however, lies in the low predictive value. Only in combination with biochemical markers, this evaluation is clinically relevant for a preventive therapy. In the second trimester, the combination of Doppler sonography and angiogenic factors such as PlGF/sEndoglin (sEng) and sFlt-1 is a valid prediction of preeclampsia [44].

In order to intervene preventively, high-risk population should be identified before the 16th week of pregnancy. The aim is, therefore, to predict preeclampsia at the first trimester of pregnancy.

PAPP-A was first identified as a predictive marker. PlGF is also in the first quarter of pregnancy decreased. Further promising targets for the first-trimester screening are PP-13, soluble endoglin, inhibin A, activin A, pentraxin 3, P-selectin, IGFBP-1 and IGFBP-3, adiponectin, resistin, l-arginine, asymmetric dimethylarginine (ADMA), and homoarginine. However, sFlt-1 is not suitable for screening in the first trimester [34].
