The placental growth factor (PlGF) and its soluble receptor (sFlt-1) are circulating angiogenic factors. During pregnancy these factors are released by the placenta into the maternal circulation. Preeclampsia affects 2-7% of pregnant women according to their risk factors and is characterized by high blood pressure and the onset of de novo proteinuria in the second half of pregnancy. Alterations of the sFlt-1/PlGF ratio in preeclampsia correlate with the diagnosis and adverse outcomes, particularly when the disease presents prematurely (<34 weeks). These factors can be assayed in maternal blood and measuring the sFlt-1/PlGF ratio is now available. We propose in this work to update the knowledge of these two molecules, describe their roles and evolution during normal pregnancy and preeclampsia, and finally to focus on the available assays.