Answer
Amniocentesis and chorionic villus sampling(CVS) are two procedures that are used during pregnancy to check for genetic diseases and abnormalities in fetuses:
Amniocentesis is usually performed between the 14th and the 18th week of pregnancy.
CVS can be performed as early a the 8th week of pregnancy, but the 10th week is considered the optimal period.
The Procedures:
In amniocentesis a long needle attached to a syringe is inserted into a pregnant woman's abdomen, and under ultrasound guidance directed through the wall of the amniotic sac into the amniotic cavity. A small amount of amniotic fluid is aspirated --about 10-15 ml--is usually with drawn.
In CVS, under ultrasound guidance, a catheter or tube is passed through the cervical canal and vagina to make contact with the villi of the chorion. Small pieces of the chorionic villi are suctioned off into the tube and then used for genetic and chromosomal testing and examination.
Work Step by Step
The tests : Amniocentesis:
In the case of amniocentesis the fluid is tested for chemical markers of abnormal genetic conditions. Sloughed off fetal cells in the fluid are also tested. These cells are cultured in the lab and then the cells examined for DNA abnormalities. Karyotyping of these cells is also done to check for chromosomal abnormalities.
Tests done on materials from amniocentesis may give indications of the following fetal abnormalities:
Down's syndrome, Klinefelter's syndrome, sickle cell anemia, cystic fibrosis, Tay Sach's Disease and spina bifida.
Materials obtained by both procedures can be used for chemical tests and chromosomal examination. In the case of CVS however karyotyping can be done almost immediately after the sample is obtained, while in the case of amniocentesis it takes several weeks of culture before enough cells are available for karyotyping.
Some conditions and chromosomal abnormalities detectable by CVS tests include:
Down's syndrome, Klinefelter's syndrome, Duchenne muscular dystrophy, phenylketonuria (PKU), fragile X syndrome,and cystic fibrosis.
