The purpose of this study is to investigate a new method of studying the health of unborn babies using amniotic fluid. Amniocentesis is often performed after maternal CMV infection to diagnose fetal infection. Prior research by Dr Hui has demonstrated that cell free RNA in amniotic fluid can provide meaningful information from multiple organs including the fetal brain. The investigators propose to collect and analyse a small sample of amniotic fluid to detect which genes are turned "on" or "off" (gene expression) in a fetus that has a congenital CMV infection, compared to those without any infection.