Some mRNA concentrations are observed to increase in the maternal circulation in association with pre-eclampsia, including placenta-specific 1 (PLAC1) and pregnancy associated plasma protein A (PAPP-A), which were previously proposed as predictive markers for pre-eclampsia. Here, we investigated their concentrations in early-onset and late-onset pre-eclampsia maternal plasma to determine whether different mechanisms are involved in these two forms of the disorder.