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Amniocentesis What is amniocentesis? Amniocentesis is where a needle is passed into the woman’s womb and some fluid removed from around the baby. The whole test is done using ultrasound so as the needle can be accurately guided into the fluid. Why do people have amniocentesis? The main reason for having an amniocentesis are as follows;

  • Certain women have an increased chance of giving birth to an infant with a chromosome problem e.g. Down’s syndrome due to either their age, previous pregnancies or tests within pregnancy.
  • There may be a personal or family history of a genetic problem which can be diagnosed whilst the baby is still at a very early stage of pregnancy
  • There may be a problem identified with the baby on the ultrasound scan which needs further tests.
  • There may have been a problem with the chorionic villous biopsy where the result was unreadable.
  • Some women just wish to know for definite that their baby does not have Down's syndrome.
Is amniocentesis used for reasons other than genetic testing? Amniocentesis can be done from 15 and a half weeks of pregnancy for a variety of reasons. We may test the fluid in cases where you have antibodies which may be destroying the baby’s blood cells. Other times we may test the fluid to see if the baby has an infection. Are there any special preparations or precautions for amniocentesis? The ultrasound picture of the baby is often clearer if the woman has a full bladder. This means not going to the toilet for 2 hours before the examination. Try to drink only 2 to 3 cups of fluid during that time. If you really feel the need to go to the toilet try to only half empty your bladder. After the CVS you should avoid hard activity but you donot have to rest in bed or a chair for the rest of the day! How is amniocentesis done? After having had everything fully explained to you, you will be asked to lie on the bed. An ultrasound machine is then used to look at the baby and womb. The doctor then decides as to where best to place the needle. Then your tummy is cleaned with a cold cleaning fluid and some green sheets placed around your tummy. Because the needle is so fine no local anaesthetic (pain killing drug) is used - it would hurt you more to have the local anaesthetic needle! The amniocentesis needle is then gently pushed through your skin into the fluid around the baby. This is all done using ultrasound to check where things are positioned. A syringe is then attached to the end of the needle and about 15 mls of fluid is removed. The needle will be in place for approximately 30 seconds. After the needle is taken out the baby will be looked at again on the ultrasound. Occasionally, two attempts are needed to get the needle into womb. There is no way to predict if this will happen to you but usually it is rare. Your partner can be present with you at all times but it is best not to have children in the room during the test. Will amniocentesis hurt my baby? The test should not harm your baby. The needle used is kept well away from the baby. If the baby should move up against the needle they will move away on touching it. The needle used has a sharp internal part which is removed once the needle is in the fluid around the baby. This then only leaves the blunt part of the needle in the womb. Also, the needle is so fine that even if it did puncture the baby’s skin no permanent damage would be done other than an occasional little pin prick mark. How soon is the fluid replaced in the womb? The baby makes the amniotic fluid by passing urine and from some fluid escaping across the baby’s skin. Within a day the fluid removed is replaced. The volume of fluid around the baby is about 150 mls at 15 weeks pregnancy but about 1000 mls at 28 weeks pregnancy. How much pain is involved with amniocentesis? Most women will feel a slight pressure or even a menstrual-like cramp when amniocentesis is performed. It is rare to feel anything more than this. What are the problems with amniocentesis? Immediate problems Cramping may occur during amniocentesis and for a short while afterwards. This does not mean that you will have a miscarriage. Bleeding and leaking of fluid from the vagina rarely occurs but if it does you should contact your doctor, midwife or genetic counsellor.

Miscarriage.
By the time of 14 weeks, the chance of having a miscarriage without having an amniocentesis is about 2%. An amniocentesis will increase this chance by half a percent. Therefore if you do miscarry after the test it is more likely that you were due to miscarry than the test actually causing the miscarriage. Generally, the more experienced the doctor, the lower the chance of miscarriage. If you are to miscarry this mostly occurs within the first 2 weeks after the test.. By the time of 14 weeks, the chance of having a miscarriage without having an amniocentesis is about 1 - 2 %. An amniocentesis will increase this chance by half a percent. Therefore if you do miscarry after the test it is more likely that you were due to miscarry than the test actually causing the miscarriage. Generally, the more experienced the doctor, the lower the chance of miscarriage. If you are to miscarry this mostly occurs within the first 2 weeks after the test.

Infection.
This is very rare. If this is going to happen, it usually occurs within 24 to 72 hours after the amniocentesis.

Repeat testing needed.
Repeat testing needed. Very rarely the specialist may not be able to obtain amniotic fluid, or the laboratory analysis will fail to yield results. This does not mean that something is wrong with you or your baby. The test can be repeated but the chance of miscarriage is increased each time a needle is put into the womb by about half a percent or 1 in 200 pregnancies. What about the results? The results are made from examining the skin cells of the baby found in the amniotic fluid removed during the test. These skin cells are found in the fluid as the baby is constantly losing skin cells just like we do everyday. These cells have to be grown in the laboratory to get a result. This is different from chorionic villous biopsy where the cells are from the placenta or afterbirth. How long does it take to get results? The result for trisomy 21 takes 72 hours to come back. This is called the PCR test. This result can be regarded as being as close to 100% accurate as possible. We also return a quick result for two other chromosomes 13 and 18. If the result for the three chromosomes is normal then the chances of any other problems being detected on the full growth result some 2 weeks later is less than 1 in 200. If the test results are normal, will my baby be healthy? There is no test available that absolutely guarantees you will have a healthy baby. The chances of the test not detecting a chromosomal problem if there really is one present is extremely rare. Sadly, nothing in life is absolutely 100% true. If we tell you that the test is abnormal or normal then the chances of the test being wrong is extremely rare - less than 1in 10,000 tests. What happens if the test results are abnormal? You will be telephoned by the doctor about the test results. An appointment will then be made for you to discuss these results with the appropriate person. Are the results really easy to understand? Yes as rule they are. However, occasionally about one in 500 tests show a combination of both normal and abnormal cells. This can be difficult to understand and may need a further test where we take some of the baby’s blood from the umbilical cord whilst the baby is still in your womb. Sometimes we have to take blood from both you parents of the baby to try and work out what the result of the test means. Can you tell the sex of the baby from the test? Yes it is possible to tell the sex of the baby but we will only tell you if you ask us. Why is it important to know your blood type and Rhesus status? If you are Rhesus negative you will need to receive a medication called Anti D after the chorionic villous biopsy is performed. Anti D is a medication which can prevent the problem of the baby's blood cells being destroyed by your immune system in future pregnancies. If the baby's father is also Rhesus negative, you will not need to receive Anti D. If you are Rhesus negative, ask your midwife or doctor to supply you with information about what it means to be Rhesus negative.