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A. Chorionic villus sampling (CVS) and amniocentesis are diagnostic tests.
These diagnostic tests can tell if your baby definitely has a serious condition by checking their chromosomes for genetic information.
CVS and amniocentesis are both invasive tests. Invasive tests involve taking a sample from within the woman’s body.
A. You will be offered a CVS or amniocentesis if:
A. You can ask for more information and do not have to decide straight away. It is your decision. You can choose to have:
Your obstetrician will discuss with you:
If you decide not to have a CVS or amniocentesis, you can still have all other parts of your routine antenatal care. Your obstetrician will explain what this means for you.
A. If you decide to have a CVS or amniocentesis, you will need to bring someone with you. It is safe to eat and drink as normal before and after the procedure.
You may need to have a full bladder when you come for the appointment. You will be given specific instructions. Both procedures usually take around 10 minutes to perform. Your appointment may be longer to allow time to discuss the procedure beforehand and to rest afterwards.
A. If you have a CVS, we take a tiny sample of tissue from the placenta (placental tissue) for testing. The sample contains some of your baby’s cells which contain genetic information (DNA).
CVS is usually done from weeks 11 to 14 of pregnancy but can be done later. If the doctor decides it is not safe to do the procedure at a particular time, they may offer you another appointment 7 to 14 days later when the placenta will be larger and easier to reach.
CVS can be performed:
The transabdominal method is more common because it is often easier to carry out.
Transcervical CVS is also more likely to cause vaginal bleeding immediately after the procedure, which occurs in about 10 in every 100 women who have this procedure.
There is no difference in the risk of miscarriage between the 2 methods.
Transcervical CVS may be preferred to transabdominal CVS if it is easier to reach your placenta this way.
After taking the needle out, your baby is observed for a short time on ultrasound.
A. You will get a rapid CVS result in about 3 days. If this confirms what was seen during your scan, your doctor will discuss your options with you straight away.
If your scan did not show anything unexpected, we recommend waiting for the second CVS result, within 2 weeks, before making a decision about whether to end your pregnancy.
This is because of a rare condition called confined placental mosaicism (CPM ) in which the DNA in the placenta is not the same as the baby’s. The second CVS result reflects the DNA of the baby rather than the placenta and is not affected by CPM.
If your ultrasound scan showed your baby may have a physical condition, your doctor will discuss your options after the rapid CVS result, rather than recommending that you wait.
A. If you have an amniocentesis, we take a small amount of amniotic fluid (the water around your baby inside your uterus) for testing. The sample contains some of the baby’s cells, which contain genetic information.
Amniocentesis is usually done between 15 and 20 weeks of pregnancy, but it can be done later.
We clean your abdomen with antiseptic and may use a local anaesthetic injection to numb a small area. We insert a fine needle through your abdomen and into your uterus to take the sample. We use an ultrasound probe to guide the direction of the needle.
Occasionally, for fewer than 7 in every 100 women, we cannot take enough fluid at the first attempt and have to re-insert the needle. This is usually due to the position of your baby.
If a second attempt fails, we will offer an appointment to have the amniocentesis again on another day.
After taking the needle out, the baby is observed for a short time on ultrasound.
Amniocentesis results are usually available in around 3 days. They are a true reflection of the baby’s DNA.
A. Most women say that CVS or amniocentesis is uncomfortable rather than painful. Some say it feels something like period pain.
A. You can have a CVS or amniocentesis if you are pregnant with twins.
CVS or amniocentesis in twin pregnancies is more complicated and should be performed in a specialist unit. The doctor may need to insert the needle twice to get samples of placenta or fluid from each baby. With CVS
there is a small chance of getting 2 samples from the same baby, which could give misleading results.
The risk of miscarriage when having CVS and amniocentesis with twins is about twice as high as in single pregnancies. If this occurs, it may lead to the miscarriage of both babies.
A. If your blood group is Rh (rhesus) negative, it will be recommended that you have an injection of anti-D immunoglobulin after the procedure to prevent you from developing antibodies against your baby’s blood cells.
If you are HIV positive, CVS or amniocentesis might increase the risk of passing HIV on to your baby. You should talk to your obstetrician to decide what is best for you and your baby.
If you have hepatitis B or hepatitis C viruses, CVS or amniocentesis might increase the risk that you pass this on to your baby. The obstetrician caring for you will be able to offer further advice.
A. The hospital will send the sample of tissue from your placenta (CVS) or amniotic fluid (amniocentesis) to a laboratory for testing.
Depending on the type of laboratory test, you will usually receive 2 results, the first after 3 days and the second after 2 weeks.
In most cases the result will let you know, one way or the other, whether your baby has the condition the test was looking for.
Most CVS or amniocentesis results show babies do not have the condition the test was looking for.
Some women will be told their baby has the condition the test was looking for.
Very occasionally, women have a CVS or amniocentesis test to detect Down’s syndrome, Edwards’ syndrome or Patau’s syndrome and the test detects a different condition.
A CVS or amniocentesis test result which shows a baby does not have the conditions tested for, rules out most conditions, but not all.
If the result shows your baby has the chromosomal or genetic condition being tested for, your obstetrician will talk to you about what this may mean for you and the baby.
If the result shows that your baby has a condition, you should be able to talk to a consultant paediatrician, consultant geneticist or genetic counsellor.
You might choose to continue with your pregnancy or end the pregnancy (have a termination).
If you decide to continue with your pregnancy, your doctor will discuss your care and how best to care for your baby during pregnancy and after birth.
If you decide to end your pregnancy, you will be given information about what this involves and how you will be supported. This will include the