Prenatal Diagnosis

There are a number of ways of testing to find out if an unborn baby has inherited a genetic defect of haemoglobin and a disease such as sickle cell disease and thalassaemia major. These tests are called pre-natal diagnosis or PND for short. These will identify the type of haemoglobin that the unborn baby has inherited from both parents.

Types of Test Available

The type of test that is offered will depend on how many weeks pregnant the woman is. There are three types, these are chorionic villus sample (CVS), amniocentesis and fetal blood sampling (FBS). These tests are done in a regional testing Centre or hospital as a day admission and local anaesthetic may or may not be used.

The sample that is tested is not taken from any part of the baby’s body and in all these tests there is a 0.5 - 1% risk of miscarriage as a result of having the procedure done.

Prenatal Diagnosis

  • Chorionic villus sample (CVS)
    This test can be done after 10 weeks of pregnancy. A small piece of the placenta (the afterbirth) is taken and sent for testing. The result is usually available within one week.
  • Amniocentesis
    This test can be done from around 14 weeks of pregnancy. A small amount of the liquid around the baby, called amniotic fluid, is taken and sent for testing. The result is usually available within one week.

    In both of these tests, Chorionic villus sample and Amniocentesis, but there is increased risk of miscarriage of about 1% as a result of these diagnostic tests. The risk calculation does not take into account the background miscarriage rate which may occur even in women who have not had any procedure done.
  • Fetal blood sample (FBS)
    This test can be done around 16 weeks of pregnancy, but can be done up to delivery of the baby. A small amount of blood is taken from the cord and sent for testing. This is rarely offered as it has a higher risk of miscarriage than the other diagnostic tests above. The result is usually available in two to four days.

    The sample for all these tests is not taken from any part of the baby’s body.

Planning for testing of the unborn baby

Women at risk of having a baby with a genetically inherited disease of haemoglobin are advised to discuss the options available before becoming pregnant, so that they will have a chance to find out as much as possible about these tests before hand. Further information about these tests is available from the family GP, practice nurse, health visitor, genetic counsellor or specialist nurse at one of the specialist National Sickle Cell / Thalassaemia Centres.

It takes a few days to arrange for these tests to be done, therefore, it is important to make contact with the health care workers as soon as a pregnancy has been confirmed in order to arrange testing as early as possible.

The decision to have a pre-natal test rests with the individual woman and her partner. The health care workers are there to offer information that will help them whilst they are trying to reach a decision, they will not influence them to make a decision either way.

If the test result is positive

Most women and couples would have considered what they would do if the prenatal diagnosis test shows that an unborn baby has the genetic disease that it is being tested for. It could be that they decided to have the test in order to prepare for the arrival of an affected child; or in order to avoid having a child or another child with the genetic disease or they were planning to avoid having an affected and consider termination.

In either case, it is useful for the woman and her partner to discuss their options the options and possible outcomes and how they are feeling emotionally about the decision they are trying to make with their GP, midwife, health visitor, genetic counsellor or nurse specialist who are available to support them.

If the woman and her partner decide to terminate the affected pregnancy this will be arranged for them; however if they decide to continue the pregnancy their decision will be respected, they will be given as much support as they need irrespective of the decision they make.

There are self help groups and other agencies who offer support in situations like this, they are independent of the specialist centres and are usually made up of people who have been through a similar experience themselves. For example, Antenatal Results and Choices (ARC) (www.arc-uk.org) they can be contacted on Tel: 020 7631 0285 and DipEX a website which gives personal experiences of disease and illness (www.dipex.org).

Other available options

Pre-implantation genetic diagnosis (PGD)

Pre-implantation genetic diagnosis (PGD) is another possible option for couples who do not want to have a child with sickle cell disease yet feel, for whatever reason that they are unable to consider termination of an affected pregnancy. This option is only available for those at risk of having a child with sickle cell anaemia only, see Pre-implantation genetic diagnosis (PGD).