RNA samples of patients with confirmed diagnosis of PE and controls were labeled using indirect labeling method. Briefly, 1μg of total RNA was reverse transcribed. The cDNA then undergoes second strand synthesis and clean-up to become a template for in vitro transcription (IVT) with T7 RNA Polymerase. During IVT, the modified nucleotide, 5-(3-aminoallyl)-UTP (aaUTP) was incorporate into the cDNA. After that, fluorescent Cy3 was chemically coupled to aaUTP which contains a reactive primary amino group on the C5 position of uracil. The dye incorporation rate was assessed with a Nanodrop ND-1000 spectrophotometer and was found to be between 1.2 and 1.4 pmol/μl. Hybridization was carried out using the Agilent oligonucleotide microarray in situ hybridization plus kit (p/n 5184-3568), fol-lowing the manufacturer's instructions. Briefly, 750 ng of Cy3 labeled sample cDNA was subjected to fragmentation (30 min at 60°C) and then hybridization on 44K Human Whole-Genome 60-mer oligo-chips (G4112F, Agilent Technologies) in a rotary oven (10 rpm, 60°C, 17 h). Slides were disassembled and washed in solutions I and II according to the manufacturer's instructions.