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This is a procedure used to draw a sample of amniotic fluid that surrounds and cushions the baby in the womb. This fluid contains cells that are normally shed from the skin of the fetus. The fetal cells are extracted and then tested in the laboratory.
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| Amniocentesis is commonly done to diagnose common chromosomal defects, of which Down's syndrome is the most common. Women with increased risk include those who are 35 years old or above and women with a family history or a child with a chromosomal disorder. Sometimes it is done later in the pregnancy to test for chromosomal disorders when an ultrasound scan shows an abnormality. |
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| When is amniocentesis done? |
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| Amniocentesis can be performed at any time during the pregnancy after 15 weeks gestation. Traditionally, it is performed at 16 weeks of pregnancy. A similar test, called chorionic villous sampling (CVS) is sometimes used to detect similar abnormalities. Instead of sloughed foetal cells, CVS examines placental cells, which are genetically similar to the fetus. Since CVS can be done earlier in the pregnancy, it may be preferable for women who need quick answers about their baby's health. However, CVS carries a higher risk of miscarriage than amniocentesis. |
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| What are the risks of amniocentesis? |
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| About one in 200 (0.50%) women has a miscarriage as a result of amniocentesis, over and above the normal rate of miscarriage. Rarely, (less than one in 1,000) women develop a womb infection (or chorioamnionitis) after amniocentesis. A recent audit at FMGC showed a miscarriage rate of 0.3% (one in 300 cases). |
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| A miscarriage may start with leakage of water (amniotic fluid) or bleeding (spotting to clots with severe abdominal pain) from the vagina. |
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| Another risk of amniocentesis is the possible development of a Rhesus iso-immunisation if you are Rh-negative. To prevent this blood disorder from developing, an injection of Rh immune globulin (RhoGam) is given within 36 hours after amniocentesis, to those who are Rh-negative. |
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| How can I prepare for the test? |
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| Amniocentesis is used strictly to diagnose problems during pregnancy - it does not treat these problems. Some birth defects are incompatible with life, others are easily corrected, and still others fall somewhere in between. When amniocentesis is done for a structural abnormality detected by ultrasound, the results will be able to help determine the outcome of the pregnancy. |
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| This means that the doctor will be able to advise and predict the outcome for the baby. For example, if the amniocentesis result shows an abnormality in the chromosome, the outcome for the baby can be worse than if it is normal. With this information, the doctor will be able to advise how the labour and the rest of the pregnancy should be managed. |
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| If the decision is to proceed with the amniocentesis, the doctor will give detailed instructions on how to prepare for the actual procedure. This test does not require an overnight stay in the hospital. It does not require a general anaesthetic. There are no fluid or food restrictions. You and your husband/partner would be asked to sign a consent form before proceeding with the test. |
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| What will happen? |
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| An ultrasound is first done to verify the gestational age of the pregnancy and confirm any structural abnormalities in the fetus. It will also allow to pin-point the exact position of the fetus and placenta the safest place to insert the needle can be determined. |
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| The doctor will clean the skin with a cold antiseptic. Guided by the ultrasound, a narrow, hollow needle is inserted through the abdomen, into the amniotic sac. About four tablespoons (1 ml per week of gestation; therefore 16 weeks = 16 mls) of amniotic fluid is then drawn up into a syringe. The needle is then withdrawn and a little plaster or cold spray (Op-site) is applied to the site. An ultrasound is then performed to ensure that the baby is okay. The baby very quickly replaces any fluid that is taken. |
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| If a local anaesthetic is used, you may feel a stinging sensation for a few seconds. You may also feel slight pain or cramps when the doctor inserts the needle. You may also feel pressure in your lower abdomen when the fluid is being withdrawn.
The doctor then extracts about four tablespoons of amniotic fluid. This fluid contains foetal cells that a technician grows and analyses in a lab. Test results are generally available in 10 to 14 days. However, if QFPCR (Quantitative Flourescent Polymerase Chain Reaction) or FISH (Fluorescent In-Situ Hybridisation) is done, the results is available in 2-3 days.
Your husband, partner, relative or close friend may stay with you during the test if you wish. |
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| Amniocentesis is done in an examination room, either with or without local anaesthesia. It typically takes just a few minutes, during which you must lie very still. The doctor locates the best pool of liquor with an ultrasound. Using the ultrasound for guidance, the doctor carefully inserts a long, hollow needle through your abdomen and into the amniotic sac. |
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| The doctor then extracts about four tablespoons of amniotic fluid. This fluid contains foetal cells that a technician grows and analyses in a lab. Test results are generally available in 10 to 14 days. |
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| What happens to the sample? |
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| The fluid obtained is kept and transported in a sterile plastic container and sent to the laboratory for analysis. Fetal cells are extracted from the amniotic fluid and they are grown (cultured) and then analysed. Depending on what test is done, the sample is sent by special courier either locally or abroad. |
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| When will the results be ready? |
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| The turn-around time is 8 to 10 days but it may take up to 2 weeks. You will be informed as soon as the result is ready. Very occasionally (about 0.5%), the cells in the amniotic fluid cannot culture. When this happens, a further sample may have to be taken. |
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| In cases where a rapid diagnosis of certain chromosomal abnormalities is needed, a procedure called FISH (fluorescent in-situ hybridisation) can be done. However, this is limited to the most common chromosomal abnormalities such as Trisomies 21, 18 and 13 and problems with the sex (X and Y) chromosome. The test costs more but the results can be ready in 1 to 2 days. |
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| What are the do's and don'ts after the test? |
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| Amniocentesis is done on an outpatient basis and does not require hospitalization. It takes only a couple of minutes. You do not require any close monitoring or observation afterwards and you would be allowed home after the procedure. It is advisable to rest for the remainder of the day. However, it is not necessary to go to bed but you should avoid physical strain (such as carrying heavy lifting or strenuous exercise). You will be given two days off work. |
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| It is normal to experience lower abdominal discomfort after the test. However, if you experience any abdominal pain, vaginal bleeding or leakage of fluid, or any signs of infection such as fever or chills, you should call your doctor immediately. |
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| Try not to worry while waiting for the results. Over 95% of women will have a normal test result. |
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| Who should have amniocentesis? |
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| Amniocentesis is typically offered to women at increased risk for bearing a child with birth defects. This includes women who: |
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- Will be 35 or older when they give birth. (chromosomal disorders such as Down's syndrome and other genetic abnormalities increases with increasing age)
- Have a screening test or examination result that indicates a possible chromosomal or birth defect (such as a positive double or triple screening test).
- Have a family history of genetic disorders. (If birth defects run in your family, seek genetic counseling before you have amniocentesis - and if possible, before you get pregnant. Certain blood tests can be performed on you and your partner to determine your chances of having a baby with a birth defect.)
- Have had chromosomal or birth defects in previous pregnancies.
- Have a structural abnormality on ultrasound scan
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