The chorionic sac encompasses the fetus and the amnion and is covered with chorionic villi until the 8th week. After the 8th week, these villi are constricted due to a decreased blood supply until ...

[2]#2 During that anatomy scan, your provider may be able ... If you have a higher-risk pregnancy, your doctor may recommend a chorionic villus sampling (CVS), done between 10 and 13 weeks ...