MATERIALS AND METHODS

The study was performed in two stages. Initially, placental tissue gene expression profiles in both the first and third trimesters of pregnancy were systematically identified using oligonucleotide micro-arrays. This was followed by the development of a number of assays based on real time quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) for the detection of six of the identified placental expressed genes in maternal plasma. The RNA transcripts studied were assessed both for their detectability in maternal plasma, and the correlation of their levels between plasma and placental tissues. All placental and blood samples used in this study were collected with informed consent from healthy women with uncomplicated singleton pregnancies, who attended the Department of Obstetrics and Gynaecology at the Prince of Wales Hospital, Hong Kong. The study was approved by the Clinical Research Ethics Committee.