Genetic testing is a process by which the developing baby is assessed for inherited or problematic conditions such as Down's syndrome, cystic fibrosis, thalassaemia or haemophilia.
Not all woman are offered genetic testing. It is usually done if the screening tests undertaken in earlier pregnancy - comprising ultrasound scans, blood tests and serum screening - reveal that the baby is at high risk of an abnormality.
Additionally, genetic testing will be undertaken if there is a family history of chromosomal abnormality. Older pregnant women – those in their late 30s and 40s – may also be offered genetic testing.
There are two main methods for conducting genetic testing, comprising amniocentesis and chorionic villus sampling.
Amniocentesis involves removing a small amount of the amniotic fluid that surrounds the fetus. This contains skin cells from the baby and can be tested for chromosomal defects such as Down's syndrome or genetic disorders such as cystic fibrosis.
It can only be performed from 15 weeks of pregnancy, and carries a one per cent risk of miscarriage.
Chorionic villus sampling (CVS) is the process by which a small amount of tissue is taken from the placenta. This is known as chorionic villi.
The sample is then examined for both chromosomal abnormalities and genetic disorders. CVS can detect issues such as Down's syndrome, muscular dystrophy and sickle-cell anaemia.
CVS can be performed from 11 weeks and carries a one-two per cent risk of miscarriage.
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