We focused on the detection of microRNAs in maternal circulation during the course of physiological pregnancy. We tested initially microRNAs (mir-135b and miR-517a) which presence in maternal circulation had been previously demonstrated and those microRNAs (miR-518b and miR-517a) with up-regulated expression profile in placentas derived from pregnancies during the onset of preeclampsia.
Further we selected those microRNAs, which were reported to be placenta specific according to the miRNAMap database (these microRNAs were significantly expressed in the placenta and simultaneously showed no or minimal expression in other tissues).