Genetic Screening is the process of checking an individual for signs of genetic diseases or defects. Ideally, this is usually performed before a child is born in order to determine the genetic defects, if any the unborn child carries. The parents may then decide if an abortion should be carried out with advice from a doctor.
There are two main methods of carrying out genetic screening, namely amniocentesis and chorionic villus sampling. In chorionic villus sampling, a fine catheter is passed through the vagina and cervix and through the placenta where the chorionic villi are located. A small sample of cells is carefully extracted. These cells are genetically identical to the fetus as they are derived from the zygote. Therefore these cells can be studied and checked for any defects. This method can be used very early during pregnancy,(8-12 weeks) but there is a greater risk of a miscarriage.
In amniocentesis, a thin needle is passed through the abdomen and about 20cm3 of amniotic fluid is taken out. A local anesthetic is needed in this case. Again, the cells of the amniotic fluid contains cells derived from the zygote and so screening of these cells will be able to determine if any genetic defects are present. Amniocentesis must be performed later on in the pregnancy than in chorionic villus sampling but there is less of a risk of having a miscarriage.