An amniocentesis — also known as an amnio — is a type of prenatal test that can detect and diagnose chromosomal conditions. The results of the test can provide you with valuable information about your baby and help you and your partner make decisions about her health. Show
Not every expecting mother-to-be will need this test, however. Here’s what you need to know about amniocentesis and how to determine whether it’s right for you. What is an amniocentesis?An amniocentesis is a procedure that extracts amniotic fluid (i.e., the fluid that surrounds your baby) from the uterus. This fluid, which contains your baby’s cells and other chemicals, can provide a wide range of information about her genetics, health and level of maturity. Amniocentesis can detect several hundred genetic conditions, including Down syndrome, Tay-Sachs and sickle cell anemia. Unlike chorionic villus sampling (CVS), in which a sample of tissue is taken from the placenta, an amnio can also rule out neural tube defects such as spina bifida. An amnio does not, however, detect every kind of abnormality, including cleft lip or palate. And it can't determine the severity of the problem. Why is an amniocentesis performed?Like all genetic testing, amniocentesis is optional. It is generally offered when:
When is an amniocentesis done during pregnancy?Amniocentesis is usually performed between week 16 and week 20, though it can be performed up until you give birth. (It’s not recommended before week 15 because there are risks involved, including miscarriage.) Do amniocentesis tests carry risks?The risks from amniocentesis — to both you and your baby — are rare. However, some complications that can occur include:
What happens during an amniocentesis procedure?You'll lie flat on your back for this procedure, with a drape placed over you, leaving just your belly exposed. Your abdomen will be cleaned with an antibacterial solution to prevent infection. An ultrasound will be performed to locate the position of the amniotic sac along with the fetus and placenta so your doctor can steer clear of them during the procedure. A long, very thin, hollow needle is inserted into your abdomen and uterus, into the fluid-filled amniotic sac. Your practitioner will be looking for a spot away from the baby, where there is a good pocket of fluid to withdraw — about two tablespoons are all that's needed. (Don't worry, your body will quickly produce more amniotic fluid to replace what's withdrawn.) You may feel a sting from the needle, and some pain and cramping, but this is normal and tends to be mild. If you're carrying multiples, your practitioner may need to perform the procedure more than once to take a separate sample from each baby. If you're Rh negative (which is determined through Rh factor testing), you'll be given an injection of Rh-immune globulin (RhoGAM) after amniocentesis to be sure the procedure does not result in Rh problems. From start to finish, an amnio takes about 30 minutes (though most of the time even less), but most of that is the setup and ultrasound — the needle-sticking part only takes a couple of minutes. After the procedure, you'll be able to drive yourself home, though some doctors recommend that you have someone else there to drive you just to be on the safe side. You'll probably be told to take it easy for a few hours to a full day. You may wish to avoid sex, heavy lifting, strenuous exercise and flying for the next one to three days. How accurate are amniocentesis tests?The results from an amniocentesis tend to be accurate. For example, the test is more than 99 percent accurate in diagnosing Down syndrome. Interpreting your amniocentesis test resultsAmnio results are available within one day to several weeks. Labs that offer the FISH — fluorescent in situ hybridization — method, which quickly counts the number of certain chromosomes within cells to get a faster result, can come back within a day or two. It's always followed by the usual chromosome analysis in the lab. Results of amnio that's performed any time during the last trimester to assess the maturity of the fetal lungs are available within a day. More than 95 percent of the time, amnio will find nothing but a healthy baby. (And if you'd like to know the sex of your baby, amnio will give you that news, too.) Although most of the conditions that are detected with amniocentesis can't be cured, the test can let parents know about them in advance. This gives parents the time to become informed about a condition, as well as make decisions about their baby's future health care or make the difficult decision not to continue the pregnancy. When to call your doctor after an amniocentesisComplications from an amnio are rare, but you should discuss them with your practitioner when considering whether or not to get the test. You might experience minor cramping, but if cramps become severe or persistent, call your practitioner. Also call if you notice that you’re leaking amniotic fluid, bleeding or spotting or have developed a fever over 100.4 degrees Fahrenheit. Chances are good, though, that you won't have to worry about any of those symptoms, and you'll feel like yourself again in no time.
Amniocentesis is a test performed to assess the chromosomes of the fetus. It involves performing an ultrasound and then using the ultrasound to guide a needle through the mother’s abdomen. A small amount of the amniotic fluid which surrounds the baby is withdrawn. This is sent to a specialised genetic testing laboratory. Fetal cells within the fluid are grown in an incubator until there are sufficient cells to analyse (this takes approximately 10 days). When there are sufficient cells to analyse the laboratory will issue a result, referred to as a karyotype. It is possible to obtain a partial result within 24 to 48 hours. This is referred to as a FISH test. The laboratory charges an extra cost for this FISH test. Picture of a normal karyotype (left) and Down syndrome karyotype (right) What is the FISH Test?FISH stands for Fluorescence In Situ Hybridisation. This is a special test which can be performed on uncultured amniocentesis or CVS samples. The result is usually available with 24-48 hours. The test does not detect all chromosomal abnormalities; this FISH test specifically looks at chromosomes 21, 18, 13, X and Y. This enables the FISH test to detect most of the common chromosomal abnormalities, particularly Down syndrome. The FISH test is also able to determine the sex of the baby. Unfortunately this test does not attract a Medicare rebate and the laboratory will issue an extra charge for performing this test. If the FISH test is normal, then this means that the baby is not affected with Down syndrome, and probably does not have a chromosomal abnormality, the full chromosomal analysis will still return, in approximately 10 days time. There remains a slight risk of a rare chromosomal abnormality being detected at that time. If the FISH test returns as abnormal, then this does mean that there is a chromosomal abnormality present. How do I get my results?When the results are ready, the laboratory will send these results directly to your genetic counsellor and/or doctor, who would usually communicate them to you. It is possible to definitively determine the sex of your baby from the karyotype result. What to expect on the day?An ultrasound is performed before the procedure to ensure that it is appropriate and possible to perform the Amniocentesis. The size of the fetus will be measured. The position of the placenta is then mapped and the amount of amniotic fluid assessed. Some fetal abnormalities may be visible at this stage. The amniocentesis is then performed in the ultrasound room, this test usually only takes one to two minutes to perform. Local anaesthetic is usually not given as the thickness of the amniocentesis needle is very similar to the needles used to take blood test samples (it is the thickness of a needle not its length, which accounts for the degree of discomfort). Most people say that an amniocentesis is not much more uncomfortable than having a blood test from your arm. If you have a Rhesus negative (Rh-ve) blood group then anti-D would be issued after the procedure. What should I do after the procedure?Although you are able to drive yourself home after the test most people appreciate having somebody with them to drive them home. Some patients will experience discomfort where the needle was inserted; Panadol®, Panadeine® (or other paracetamol based analgesia) or a warm pack may provide symptomatic relief. Aspirin based or non-steroidal analgesics are not advised (for example: naprosyn®; ponstan®). It is recommended that you take things quietly for the next two days. You may request a medical certificate, if necessary. After this you may return to normal duties. Are there any complications from having an amniocentesis?The risk of causing a miscarriage from an amniocentesis is quite low, no worse than 1 in 1000. The risk of miscarriage has been shown to be directly related to the skill of the operator and the number of procedures the operator has performed. Dr Bethune has had extensive experience in both amniocentesis and chorionic villous sampling and was trained by one of the pioneers of invasive fetal procedures; associate Professor Lachlan deCrespigny. Dr Bethune performs a large number of these procedures each year and is involved in teaching these procedures to obstetricians who choose to further specialize in the field of prenatal diagnosis through his commitments at the Mercy Hospital for Women. About 0.5% of patients will have some leakage of amniotic fluid through the vagina within the first 24 to 48 hours after the amniocentesis procedure is performed. 80 to 90% of these cases will resolve without any ongoing complication for the pregnancy. Although extremely rare, it is theoretically possible that the amniotic fluid does not grow properly in the laboratory and that the laboratory is unable to obtain a result. In these cases, a second amniocentesis would be offered. |