Amniocentesis
Amniocentesis is a medical procedure performed during pregnancy to obtain a sample of the amniotic fluid that surrounds the developing fetus in the uterus.
This procedure is typically carried out between the 15th and 20th weeks of pregnancy, although the timing can vary based on individual circumstances and medical recommendations.
Who is offered Amniocentesis?
Amniocentesis is typically offered to pregnant individuals who are considered to be at a higher risk of having a baby with certain genetic or chromosomal abnormalities. The decision to offer amniocentesis is often based on various factors, including medical history, age, and the results of previous prenatal screenings. The following groups of pregnant individuals are commonly offered amniocentesis:
Advanced Maternal Age: Women who are 35 years of age or older at the time of delivery are often offered amniocentesis. This is because the risk of certain genetic conditions, such as Down syndrome, increases with maternal age.
Abnormal Prenatal Screening Results: Individuals who have received abnormal results from other prenatal screening tests, such as non-invasive prenatal testing (NIPT) or combined first-trimester screening, might be offered amniocentesis to confirm or rule out genetic abnormalities.
Family History of Genetic Conditions: Pregnant individuals with a family history of certain genetic disorders or chromosomal abnormalities may be offered amniocentesis to assess the risk of passing these conditions to their baby.
Previous Child with Genetic Abnormalities: If a previous child had a genetic or chromosomal abnormality, parents may be offered amniocentesis to assess the risk of recurrence in subsequent pregnancies.
Abnormal Ultrasound Findings: Abnormalities detected on prenatal ultrasound, such as structural abnormalities or soft markers, might prompt the recommendation for amniocentesis to further evaluate the fetus's health.
Carrier of Known Genetic Conditions: Pregnant individuals who are known carriers of certain genetic disorders, such as cystic fibrosis or sickle cell disease, might be offered amniocentesis to determine if the fetus has inherited the condition.
It's important to note that the decision to undergo amniocentesis is a personal one and should be made after thorough discussion with a healthcare provider. They can provide information about the benefits, risks, and alternatives of the procedure based on individual circumstances.
How is Amniocentesis performed?
An ultrasound examination will first be carried out to confirm the age of the pregnancy, to make sure there are not twins, and to check for physical abnormalities of the fetus.
By locating the position of the fetus and placenta, steps can be taken to avoid them during the amniocentesis. Ultrasound is used throughout the amniocentesis procedure to first guide the needle to the safest position, and then to keep the needle away from the fetus. Your doctor may arrange for another scan at around 18 to 20 weeks when a more detailed check is usually possible.
When the scan has been completed the amniocentesis is performed without you having to move from the examination couch.
After cleaning the skin, a very fine needle is inserted into the uterus watching the needle all the time on the ultrasound screen. It then only takes about 30 seconds to draw the required 15 mls (3 teaspoons) of fluid into the syringe. The needle is removed and the fetus is again checked. After waiting for about 20 minutes you are then able to return home.
Patients usually feel far less discomfort from the test than they expected - many indicate that it is not even as bad as a simple blood test.
When is Amniocentesis carried out?
Amniocentesis is typically performed during a specific timeframe within pregnancy, usually between the 15th and 20th weeks. This window allows for optimal results while minimizing potential risks to both the mother and the fetus.
It's important to note that the exact timing may vary based on individual circumstances, such as medical history, risk factors, and the specific reason for the procedure.
Performing amniocentesis too early in pregnancy might result in a smaller volume of amniotic fluid, which could potentially affect the accuracy of the genetic and chromosomal analysis.
On the other hand, waiting too late in pregnancy might increase the risk of complications, such as preterm labour.
Preparation Guidelines for Your Appointment
Having knowledge of your blood group, especially your Rhesus (Rh) status, is vital prior to an Amniocentesis test. If possible, kindly request this information from your referring doctor or bring your blood group card to your Melbourne Ultrasound for Women appointment
Please be aware, if you possess a Rhesus negative blood group, you will need an anti-D injection after the Amniocentesis. Our proficient Melbourne Ultrasound for Women Obstetrician will provide you with comprehensive information about this during your Amniocentesis appointment.
When you come in for your Amniocentesis appointment at Melbourne Ultrasound for Women, having a moderately full bladder is beneficial.
This positioning elevates the uterus into the abdominal cavity, simplifying access to the uterus for the procedure. If, however, you find the full bladder uncomfortable, our skilled team will guide you to partially empty your bladder if needed.
What is done with the cells?
Amniotic fluid contains cells that have been shed by the fetus, these are sent to Victorian Clinical Genetic Services (VCGS). They are allowed to grow in the laboratory until there are enough to test the chromosomes.
Each of the chromosomes from a number of cells is carefully examined to check that the correct number are present and that the appearance and length of each chromosome is normal. The sex can also be determined by looking at the chromosomes.
The laboratory will usually have the result available within 2 weeks. Your doctor will be informed and he or she will pass it on to you. If you wish, an extra test, called FISH, can be carried out to tell you within 2 working days if Down Syndrome is present. The laboratory charges extra for FISH testing.
Understanding test risks
In a study Dr Victor Hurley carried out, including his and one other doctor’s results, the miscarriage result was not demonstrably higher than those who did not have the test performed. The risk of the test causing miscarriage therefore is very low, a best estimate is 1 in 200 or less. There is also about a 1 in 100 chance of having some leakage of amniotic fluid through the vagina after the procedure. This usually stops if you rest and it can be expected to cause no problem to the fetus or the pregnancy. If your blood group is Rh negative, anti-D is usually given. Direct injury to the fetus by the needle has not been reported after any of our patients. Rarely have any complications to the pregnant woman or other complications to the fetus been reported.
Couples often ask when a miscarriage would occur. This is a difficult question because at least two out of three miscarriages after amniocentesis are totally unrelated to the test itself and would have occurred anyway. However, if you have had no problem by three weeks then any complication is unlikely to be due to the test. The chance of complications is very much related to the experience and expertise of the operator. The test, like any other, may fail either because no specimen is obtained or because the laboratory are unable to grow the cells. Both of these are very uncommon. Incorrect results are extremely rare. Occasionally uncertain results may occur - these may need a further test such as a sample of fetal blood to sort them out.
Post Amniocentesis care guidelines
While you will be quite capable of driving yourself home after the test, most people appreciate having a companion to drive home. It is recommended that you rest for the remainder of the day although there is no reason for you to go to bed. There need be no further limitation on your normal routine after this time.
Occasionally after the test patients may have either mild discomfort or some bruising under the skin but neither causes any problem to the pregnancy.
When are you informed of the CVS results?
Dr Hurley will ring you with the Amniocentesis results as soon as they become available, and we also forward them to your referring doctor.
Fast FISH results are available in 24-48 hours. The full karyotype usually takes 10-14 days; microarrays usually take 5-10 days, and our team will call with all of your results whether they are normal or not.