PP13 is produced by the placenta and released to the maternal blood circulation. It has been shown to be an effective serum marker for early onset preeclampsia (Nicolaides KH et al., 2005). The purpose of this study is to combined the assessment of the biochemical markers with Doppler in the first and the second trimester to provide a comprehensive evaluation of various methods for sequential and combined analysis to assess the risk for developing preeclampsia.