Amniocentesis is a diagnostic test to detect a serious or potentially serious disorder in an unborn baby (foetus).
Amniotic fluid
Amniotic fluid (the fluid that surrounds the foetus in the womb) contains cells that have been shed from the skin of the developing baby, and the waste products from the baby.
Every cell in the amniotic fluid that has been from the baby contains a complete set of the baby’s DNA. Therefore, the cell samples obtained during amniocentesis are very useful for assessing the developing baby's health and diagnosing any potential problems.
Amniocentesis gives healthcare professionals direct information about how likely the baby will develop one or more of a number of conditions, which may be genetic (inherited) or develop during the pregnancy.
Results
If the results of amniocentesis indicate that there is a problem with the development of the foetus, it may be possible to treat the disorder while the baby is still in the womb.
If a serious abnormality is detected, amniocentesis enables parents to choose whether to continue with the pregnancy or terminate it at an early stage.
Conditions
Amniocentesis can diagnose many different conditions. Some of these are described below.
Chromosomal conditions
Chromosomal conditions are conditions that affect the chromosomes (the parts of the body’s cells that carry genes). For example:
- Down's syndrome – a condition that affects a person's physical appearance, mental development and learning ability; it is the result of an extra chromosome, known as trisomy-21
- Edward's syndrome – a condition that causes severe physical and mental abnormalities; it is the result of an extra chromosome, known as trisomy-18
- Patau’s syndrome – a rare but serious condition where babies rarely survive for more than a few days; it is the result of an extra chromosome, know as trisomy-13
Blood disorders
Amniocentesis can also be used to check for inherited blood disorders, such as:
- sickle cell anaemia – a condition where red blood cells (which carry oxygen around the body) are an unusual shape and texture
- thalassaemia – a condition that affects the body’s ability to create red blood cells
Neural tube defects
Amniocentesis can test for neural tube defects. The neural tube is a primitive tissue structure inside which the embryo (fertilised egg) grows during its first month of life. As the embryo develops, the neural tube changes and eventually forms the spine and nervous system.
A neural tube defect can lead to conditions such as spina bifida, which can cause learning difficulties and paralysis (weakness) of the lower limbs.
See the Health A-Z topic about Spina bifida for more information about the condition.
Musculoskeletal disorders
Amniocentesis can also be used to diagnose conditions that affect the musculoskeletal system (your bones and muscles), such as muscular dystrophy. Muscular dystrophy is an inherited condition that causes the muscles to gradually weaken, resulting in an increasing level of disability.
See the Health A-Z topic about Muscular dystrophy for more information about the condition.
Other genetic conditions
As well as helping to diagnose chromosomal conditions, blood disorders, neural tube defects and musculoskeletal disorders, amniocentesis can also be used to help diagnose a number of genetic conditions, such as Marfan syndrome. This condition affects the tissues that provide support and structure in the body.
If there is a risk of an inherited condition being passed to your baby – for example, there is a family history of the condition, then your GP, midwife or genetic counsellor will explain the risk to you and your partner. A genetic counsellor is a healthcare professional who helps people to understand and deal with genetic conditions.
