The embryo passes through three stages - (I) still enclosed within the egg and living on its own yolk; (2) free, within the vitelline mass, which is directly swallowed by the mouth; (3) there is no more vitelline mass, but the embryo is possessed of long external gills, which serve for an exchange of nutritive fluid through the maternal uterus, these gills functioning in the same way as the chorionic villi of the mammalian egg.
A urine test will detect human chorionic gonadotropin (HCG) which.. .
This risk is slightly higher with chorionic villus sampling.
Diagnostic tests Chorionic villus sampling This means taking a sample of a piece of tissue from the placenta.
Maternal blood samples were collected at prior to chorionic villous sampling.