Previous research had shown that a blood test can provide information about an unborn child, but the techniques relied on significant differences between the mother's DNA and the baby's--namely the presence of a Y chromosome--and therefore were limited to women carrying a male child. In the new work, Y. M. Dennis Lo of the Chinese University of Hong Kong and his colleagues tested blood samples from women who were between seven and 14 weeks pregnant. The researchers measured the level of fetal messenger RNA (mRNA), which is a single-stranded nucleic acid that acts as a template for protein production, in each mother's blood. They found two types of mRNA associated with genes in the placenta that code for two proteins: human placental lactogen (hPL) and human chorionic gonadotropin (beta-hCG). The levels of both types of mRNA mirrored the patterns that the corresponding placental genes are known to follow as a pregnancy progresses, and neither was detectable after the women gave birth, the team reports.
Because high levels of beta-hCG are associated with Down syndrome, the scientists hope their findings will lead to new techniques for early detection of genetic diseases. Writing in an accompanying commentary, Malcolm Ferguson-Smith of the University of Cambridge notes that the findings "indicate that the investigation of placental RNA in maternal plasma may have considerable potential for non-invasive prenatal screening and diagnosis."