Right shows a labelled diagram of an amniocentesis test with the equipment used.
An amniocentesis is not offered for those parents who wish to just know the sex of their baby however an amniocentesis test can provide a very accurate result of the sex of the baby. The sex of the baby can be important if there is an increased risk of abnormality such as muscular dystrophy which can be passed on from the mother or the father which occurs mainly in one sex which is in males. For these parents whose child may have an increased risk of abnormality it is offered as a choice.
This amniocentesis test can be carried out later on in the mother’s pregnancy to see the development of the foetus. As these amniocentesis tests are done at an early stage it gives families of the baby time to consider their options if any abnormalities are found with the development of the foetus.
Chorionic villus sampling or CVS is another test that can be done to find problems or abnormalities with the unborn foetus. It can be done earlier than an amniocentesis test at around 10 to 12 weeks, unlike the amniocentesis test where it is 15 to 20 weeks. Results for chorionic villus sampling are also ready sooner than for an amniocentesis test.
Muscular dystrophy
Muscular dystrophy is a genetic disorder in which individuals suffer slow increasing weakness in the muscles and disability. Muscular dystrophy is caused by missing genetic information that enables the muscles to develop there are chromosomes that are abnormal. The missing information in the genes prevents proteins being made that are needed for health muscles. There is not a single type of muscular dystrophy as the term means a group of genetic muscle disorders which all vary in age of when the occur and the muscles that the disorder attacks as well as the progression of the disorder. Although an antenatal amniocentesis test will be able show whether the unborn foetus has the muscular dystrophy gene, the amniocentesis test will not be able to show what type of muscular dystrophy the foetus has. It will also not show any symptoms of muscular dystrophy or how severe the type is.
The amniocentesis test will check whether the foetus has normal or abnormal levels of enzymes. These enzymes are the proteins that cause chemical changes such as converting food to energy. Abnormal high blood levels of certain enzymes from muscle cells are present in many people with muscular dystrophy. The amniocentesis examines the chromosomes in the amniotic fluid and if abnormal levels of enzymes are present then there is a chance of muscular dystrophy.
A positive test result for muscular dystrophy would be a muscle dysfunction or abnormality in the muscle fibre which release particular enzymes into the bloodstream as the muscles are weakened and therefore levels of enzymes will be higher which shows a positive test result. A negative test result for muscular dystrophy however would be as a result of there being no excessive or abnormal levels of enzymes in the bloodstream.
Haemophilia
Haemophilia is a condition that is genetic so it is inherited from family members. Haemophilia affects the blood and causes problems and impairs the body’s ability to control blood clotting. An amniocentesis test can determine whether the foetus shows any signs of lacking the blood clotting factor.
The two most common types of haemophilia are haemophilia A and haemophilia B, A is slightly more common that B. Those with haemophilia have difficulty stopping the blood flow as it is unable to clot, so when a person with haemophilia cuts or even grazes themselves the bleeding will last longer. This can lead to complications such as internal bleeding which is caused by an open wound or a deep open cut. ‘The way that haemophilia genes are passed down through family members means that almost all cases of haemophilia occur in males.’ (7) Women who are carriers of the gene that causes haemophilia can be checked by being screened to see if they are a carrier before they become pregnant so that they can be aware that their child may inherit haemophilia. Before an amniocentesis test is done to find out whether the baby has haemophilia or not the sex of the baby is found out. If the baby is male then the amniocentesis test for haemophilia will be carried out. The disorder is detected by low clotting factors in the fluid that has been taken from the amniotic sac in the uterus.
A positive result for a haemophilia test would mean that there are signs of lacking the necessary blood clotting factor. A negative result however would mean that no abnormalities have been found within the cells of the blood.
Sickle cell disorders
Sickle cell disease is an inherited disease and is when the red blood cells in the blood are shaped abnormally. Resulting from this abnormality with the red blood cells damage to the organs, chronic anaemia and infections can take place. These do however vary for individuals. Sickle cell disorders are most common among those with an African or Caribbean descent but it can affect people from Asia, eastern Mediterranean or the Middle East. Sickle cell genes must be received from both parents in order for the baby to be affected by the sickle cell disease. A sickle cell trait will be received when only one affect gene with sickle cell disease is passed on. This sickle cell trait generally does not cause any problems, but it can be passed on if they decide to have children of their own, who will develop the disease if both parents are carriers and both abnormal genes are inherited.
Sickle cell disease is the most common example of a blood disorder that is inherited. It affects the haemoglobin in the blood. The haemoglobin is the protein in the red blood cells and provides oxygen to the organs and necessary cells. As the red blood cells have changed shape from a spherical shape to a crescent shape less oxygen is able to be carried in the blood cells.
People who are sickle cell disease can need regular blood transfusions throughout their lives. A bone marrow transplant is the only known cure for sickle cell disease. These transplants are risky procedures, and are offered to patients who have severe complications due to the sickle cell disease.
The image to the left shows the normal red blood cells and the sickle cells. The blood cells that are affected by sickle cell anaemia are a different shape to the normal red blood cells.
The antenatal test amniocentesis will test for sickle cell disease, which can also be known as sickle cell anaemia. Chromosomes from the fluid took from the amniotic sac are grown and examined to check if the sickle cell disease genes have been inherited. For sickle cell disease to be inherited the foetus must inherit two abnormal genes from the parents. For a positive test for sickle cell disease a sickle cell must be found when the amniocentesis test is done. A negative test result for sickle cell disease would mean the foetus does not have sickle cell disease. Although this negative test result could be a false negative however this is rare.
