Av canal defect

Yesterday my baby was diagnosed with an AV Canal defect. The dr says that this congenital heart defect is common in babies with Down’s syndrome and other chromosome disorders but that doesn’t necessarily mean she has any of them. They want to do further testing to rule them out. Also I had a quad screening that came back negative but they said bc it’s just a screening and not a test it could have been a false negative. Anyone have any experience with this? Or can possibly offer any insight.