Amniocentesis is a prenatal diagnostic procedure in which fluid around the fetus is removed and sent to a genetic lab to diagnose chromosomal and genetic abnormalities and fetal neural tube defects.
During pregnancy, the fetus is surrounded by amniotic fluid, similar to water. Amniotic fluid contains live fetal cells and other substances such as alpha photoprotein (AFP). These materials provide important information about the health of the fetus before birth.
What happens during an amniocentesis?
It may be performed on an outpatient basis or during hospitalization. The methods vary depending on the condition of the mother and the fetus. You should remove your clothes from the waist and wear hospital clothes during the test.
It will be asked you to lie on a table with your hands behind your back. Blood pressure, heart rate, and respiration rate are monitored. Ultrasound is used to check the fetal heart rate. The abdomen is cleansed with a disinfectant. You will feel a slight burning sensation when injecting the anesthetic.
When your skin is numb, ultrasound guides a long, thin hollow needle through the skin into the uterus and amniotic sac. It may be a little painful. You may also feel cramping when the needle is inserted into the uterus.
The doctor removes a small amount of amniotic fluid through a syringe. The amount of liquid depends on the test you want to perform but usually does not exceed one ounce.
The amniotic fluid is placed in a special container protected from light and sent to the laboratory. The abdomen is cleansed with a disinfectant. After the procedure, the fetal heart rate and vital signs are checked, and a bandage is placed at the needle’s site.
What is the function of amniotic fluid, and what information does it contain?
The functions of this pale yellow liquid include:
- Protects the fetus from harm
- Allows the child to grow and move properly
- Protects against infection
- Helps control the fetal temperature
Amniotic fluid and enzymes, proteins, hormones, and other substances contain cells the fetus sheds. These cells have genetic information that can be used to diagnose genetic disorders and neural tube defects. Based on family history, they may also be used to check for inherited genetic defects and metabolic disorders.
This fluid also contains other substances that give information about the fetus. This procedure may be done in late pregnancy to check the fetus’s health and diagnose fetal health problems such as infection. If the baby is expected to be born prematurely, amniocentesis can also be done to check for lung maturity.
Fluids are sent to a laboratory to be analyzed for cells. Results are often ready in 10 to 14 days, depending on the lab. If the test is done to check the lungs’ maturity, it will be ready in a few hours.
Why is amniocentesis performed?
A complete anatomical ultrasound is performed before amniocentesis. However, a doctor prescribed this test for special conditions because it is low-risk for mother and child. These conditions include:
- Ultrasound shows abnormalities
- Family history of congenital malformations
- A pregnant mother has a child with birth defects
- Abnormal genetic test result
Amniocentesis does not detect all congenital defects, but it can be used to diagnose Down syndrome, Sickle cell disease, Cystic fibrosis, Muscular dystrophy, Tay-Sachs, and similar disorders.
What are the risks of an amniocentesis?
One of the main risks associated with amniocentesis is miscarriage in the first 23 weeks. If it is done before the 15th week of pregnancy, the risk that causes complications is higher, so the test is done only after this stage. But the risk of miscarriage after an amniocentesis in the second trimester of pregnancy is less than 1%. One in every 100 women with amniocentesis is estimated to lose their pregnancy. Some other complications of amniocentesis include the following:
- Cramping
- leaking or Bleeding of amniotic fluid from the needle puncture site or the vagina
- Preterm labor
- Infection
How accurate is amniocentesis?
It may sometimes fail due to technical problems, such as the inability to collect enough fluid or the lack of growth of contracted cells during culture. Still, overall the accuracy of this test is about 99.4%.
How do I get ready for an amniocentesis?
Your healthcare provider will explain the procedure to you. You must fill out the consent form for the test. Be careful read the form carefully before signing. In general, there are no restrictions on diet or exercise before the test.
Tell your doctor if you are allergic to medications, latex, tape, or anesthetics. Tell your doctor about all medications you are taking, especially if you are taking anticoagulants.
Make sure your healthcare provider knows if your blood type is Rh-negative. During amniocentesis, fetal and maternal blood cells can be mixed. If you are Rh-negative and the fetus is Rh-positive, this can lead to Rh sensitivity and fetal red blood cell breakdown.
Healthcare providers may be asked to empty your bladder before the operation. A full bladder helps the uterus perform a better test in early pregnancy. Still, in the last months of pregnancy, the bladder should be empty to reduce the risk of amniocentesis needle perforation.
What happens after an amniocentesis?
Your fetus’ vital signs and heart rate will be monitored regularly for about an hour after surgery. You may feel cramped during or after the operation. Tell your nurse if you feel light-headed, dizzy, or nauseous. After the test, rest at home and avoid strenuous activity for at least 24 hours.
Be sure to tell your doctor if you experience bleeding, amniotic fluid leaking from a needle or vaginal puncture, fever or chills, severe abdominal pain or cramping, and changes in fetal activity (after the 20th week of pregnancy).
Can I choose not to take the test?
Yes. Before the test, the genetic counselor talks to you and tells you the test’s advantages and risks; whether you want to take it is your choice.
What are the alternatives?
An alternative to amniocentesis is a placental villus sampling test (CVS). A small sample of placental cells is taken for testing. This test is usually done between the 11th and 14th weeks of pregnancy, although it can be done later if needed.
In CVS, the risk of miscarriage is about 1-2%, slightly higher than the risk of miscarriage for amniocentesis. However, because the test can be done sooner, there is more time to review the results. If you have been offered several tests to look for a genetic disorder in your child, a specialist can help you choose the best test.
In short, amniocentesis is a low-risk process providing useful information about many chromosomal and possible fetal abnormalities. Test results can reliably rule out or diagnose various genetic diseases, such as Down syndrome. However, amniocentesis cannot detect all genetic diseases and birth defects. If it shows that your fetus has a chromosomal or genetic disorder that cannot be treated, you may have to make complex decisions about whether to continue the pregnancy.
Additional questions
- What is the most common congenital anomaly?The most common severe congenital disorders are heart defects, neural tube defects, and Down syndrome. Although congenital disorders may result from one or more genetic, infectious, nutritional, or environmental factors, the exact causes are often difficult to identify.
- What are the three signs of preterm labor?
- Menstrual-like cramps felt in the lower abdomen
- Low, dull backache felt below the waistline
- Pelvic pressure that feels like your baby is pushing down
- What is sickle cell anemia?
Sickle cell anemia is one of a group of inherited disorders known as sickle cell disease. It affects the shape of the red blood cells that carry oxygen to all body parts. Red blood cells are usually round and flexible, moving easily through blood vessels. In sickle cell anemia, some red blood cells are sickle or crescent-shaped. These sickle cells also become stiff and sticky, slowing or blocking blood flow. - What is Tay-Sachs disease? Tay-Sachs disease is a rare genetic disorder passed from parent to child. This is due to the absence of an enzyme that helps break down fatty substances. These fatty substances, called gangliosides, accumulate in the brain and spinal cord to toxic levels and affect nerve cell function.
5. How long after amnio is there a risk of miscarriage?
Most miscarriages related to amniocentesis occur in the first three days after the procedure. It should be noted that late miscarriages caused by this method have occurred up to a few weeks after the test.
References
https://www.mayoclinic.org/tests-procedures/amniocentesis/about/pac-20392914
https://my.clevelandclinic.org/health/treatments/4206-genetic-amniocentesis
https://www.news-medical.net/health/What-is-Amniocentesis.aspx
https://www.hospitaldaluz.pt/en/health-dictionary/what-is-amniocentesis
https://www.marchofdimes.org/find-support/topics/planning-baby/amniocentesis