Maternal and fetal factors and placentation: implications for pre-eclampsia

The etiology of preeclampsia is still mysterious and a source of a variety of hypotheses. Accordingly, there is a number of theories present today describing different pathways how this disorder may develop. The most cited hypothesis on the etiology of preeclampsia is based on an inadequate remodeling of uterine spiral arteries in the placental bed due to superficial trophoblast invasion followed by placental hypoxia. Since maternal blood into the placenta is only established after week 12 of gestation, an effect of a failure in arterial remodeling can only affect the placenta starting with the second trimester of pregnancy. Recent studies on early predictive biomarkers for preeclampsia (such as PP13, fetal hemoglobin and PIGF) have indicated that there are changes of the villous trophoblast already weeks before the onset of maternal blood flow into the placenta, i.e. during mid first trimester. Moreover, a number of studies has shown that in cases with impaired trophoblast invasion resulting in inadequate remodeling of uterine spiral arteries placental hypoxia does not occur. In all these studies where mostly indirect assessments of placental oxygen have been performed, a higher oxygen partial pressure within the placenta has been measured. This is in clear contrast to the old hypothesis where placental hypoxia is essential for the etiology of preeclampsia. New biomarkers from the maternal and/or fetal compartment for the early prediction of preeclampsia may help in identifying the real etiology of preeclampsia. We need to use this momentum to decipher the real causes of this syndrome.