NHS Leeds Prenatal Family History
We understand that this may be a worrying time for you and your family. You may feel overwhelmed by the new and sometimes complex information you are receiving. As part of your care, your doctor or genetic counsellor has offered you a prenatal invasive test. This may be because you have previously had a baby with a genetic condition, or because either you or your baby’s father have a family history of a known genetic condition.
We will explain the test in detail, but more information is available from relevant patient information leaflets and through discussions with your healthcare professionals. Please feel free to take notes, and they will be more than happy to answer any questions you may have.
To understand why these genetic tests can be helpful, it’s useful to first learn a little more about your baby’s genes. Genes are the instructions that tell our bodies how to grow and develop. They are made of DNA and stored in our chromosomes. Chromosomes come in pairs, and we usually have 46 in total. They are numbered from 1 to 22, and the 23rd pair are the sex chromosomes.
When one or both parents are carriers of, or affected by, a genetic condition, they may pass it on to their children—even if they are healthy themselves. A prenatal invasive test can tell you if the known condition has been passed on to your baby.
Deciding whether to have a test is a personal choice. You may want to consider what the results may mean for your pregnancy and family. If you decide to go ahead with the test, you will be referred to your nearest fetal medicine unit. Your fetal medicine doctor may advise you on the specific test based on ultrasound findings and how easily the sample can be obtained. To minimize risks, the tests offered may depend on your personal choice and how many weeks pregnant you are. Both tests give the same results and carry the same risks.
Invasive tests carry a small additional risk of miscarriage. The national figure is one in 200, though this risk may be higher depending on your scan findings. Occasionally, it’s not possible to obtain a result, and in that case, a repeat test may be offered.
To prepare for the test:
. Eat and drink as normal
. Wear comfortable clothing
. Bring your partner or another adult for support, if desired
. If you take blood-thinning medications, discuss this with your healthcare provider before your appointment
After the test, take it easy for 24 hours. You may need to arrange work or childcare accordingly.
There are two types of prenatal invasive tests:
1.Chorionic Villus Sampling (CVS): This involves using a needle to obtain a small sample of tissue from the placenta (afterbirth). It can be done as early as 11 weeks into your pregnancy. About 1 in 10 placentas are not in a position to allow this test to be performed, which may require delaying the test.
2. Amniocentesis: This involves using a needle to obtain a small sample of amniotic fluid surrounding the baby. It can be performed after 15 weeks of pregnancy. An ultrasound scan is used throughout the test, and antiseptic will be applied to clean your abdomen. If you have a CVS, a local anaesthetic will be used to numb the skin, which may feel like a brief stinging sensation.
During the test, the needle is guided through the wall of the womb to either the placenta or amniotic fluid, away from your baby. You may feel a pushing sensation and mild tummy cramps. Once the sample is obtained, the needle is removed, and a small plaster is applied. The procedure typically takes about 5 to 10 minutes.
After the test, both you and your partner may be asked to provide a blood sample from your arm to help with the results. If you have a rhesus-negative blood type, there is a chance that your baby’s red blood cells may enter your bloodstream during the procedure. In that case, you may be offered an injection of anti-D immunoglobulin to prevent antibodies from developing, especially if your baby has a different blood group.
You can go home soon after the test. It is normal to experience some period-type cramps, which should settle with simple pain relief, such as paracetamol. You can bathe or shower after the procedure.
If any complications were to arise, they would typically occur within two weeks but may develop up to six weeks later. If you experience vaginal bleeding, watery vaginal discharge, worsening cramps, or a high temperature, contact your local maternity unit for advice and assessment.
The timing of your specific test results will be discussed with you by your doctor or genetic counsellor. Results are typically available within one to two weeks. The results will tell you whether or not the condition has been passed on to your baby. With your consent, a professional will call you to provide the results. You will also be offered testing for the most common chromosome conditions, such as Down syndrome, Edwards syndrome, Patau syndrome, and some sex chromosome changes. This test is called QF-PCR.
Deciding whether to test for these conditions will not delay your results. As with all health data, your genetic test results will be securely stored by the NHS. The results will only inform you about the tested conditions and your baby’s sex. If you wish to understand what a genetic change may mean for your baby, your doctor will discuss this with you.
You may need time to process this information. If necessary, you will be directed to UK websites and charities that specialize in this area.
If a genetic change is detected, some parents choose to continue with the pregnancy, knowing that care will be tailored to the needs of both the baby and the family. Others, after careful consideration, may decide not to continue, knowing they will be supported in their choice.
It is ultimately your decision whether to have the test or not. Your maternity care providers and fetal medicine team are here to support you. Your midwife and doctor are available to answer any questions you may have, and we hope this information helps you and your family.