What is amniocentesis? Amniocentesis is a specialized invasive diagnostic test that involves removing a small amount (usually about 15–20 ml) of amniotic fluid from the sac surrounding the fetus in the uterus. The fluid, which contains hundreds of cells from the baby's skin, can then be examined in a laboratory for chromosomal abnormalities such as Down syndrome, and to test for single-gene disorders such as thalassemia, cystic fibrosis and others.
Indications
The test is done for specific indications, such as:
- The mother's age (over 35)
- An abnormal nuchal translucency scan
- An abnormal alpha-fetoprotein or triple test
- Suspicious ultrasound findings
- A previous pregnancy with a fetus affected by a chromosomal abnormality
- Perinatal infection (toxoplasmosis, rubella and others)
- Parents who are carriers of genetic disorders such as thalassemia, cystic fibrosis and others
- At the mother's request, because of excessive anxiety about possible chromosomal abnormalities
How is amniocentesis performed? The whole procedure takes about 5 minutes. First we use ultrasound to check the basic anatomy and the size of the fetus, to confirm that the pregnancy is beyond 16 weeks, and also the position of the placenta.
The mother's abdomen is then cleaned with antiseptic solution, because the procedure is carried out under sterile conditions. A fine needle is passed through the mother's abdomen into the uterus under ultrasound guidance, and a sample of the amniotic fluid surrounding the baby is removed and sent to the laboratory for testing.
The whole procedure is carried out carefully, so that the needle keeps away from the fetus and does not injure it.
The amniotic fluid is replaced within a few hours, since it is fetal urine (99%) and the fetus goes on passing urine. At the end the fetal heartbeat is checked to make sure it is normal.
When is amniocentesis performed?
Amniocentesis gives the same information as chorionic villus sampling, and is considered safe when carried out after 16 weeks.
Does amniocentesis hurt?
Discomfort is minimal, although some women feel pain as the needle passes through the uterus. Mild cramping on the day of the test is possible.
When will I get the results of the amniocentesis?
The first results come within 2–3 days from a rapid analysis (Amnio QF-PCR), which rules out the commonest chromosomal abnormalities (Down, Edwards, Patau and Turner syndromes) and identifies the sex of the fetus. The test is completed in 10–15 days with the culture of fetal cells, which examines the fetus's entire karyotype.
The reliability of these results approaches 99.9%. At the same time the cystic fibrosis genes (ΔF508) are tested, along with the level of alpha-fetoprotein (AFP), which gives us important information about any open defects of the fetal spine.
When testing for single-gene disorders, the time needed for the results depends on how common the disorder is (for thalassemia, for example, about 3 days are needed).
What is the risk of miscarriage from this test? The uterus may be irritated by the needle and begin to contract; if the contractions persist they can cause miscarriage, intrauterine bleeding or rupture of the membranes, in 0.5–1% of cases. The
risk of miscarriage from this invasive test is about 0.5–1%, the same as for chorionic villus sampling.
The majority of women who have an amniocentesis will receive normal results, their pregnancy will continue without problems and they will give birth to a healthy baby.
INSTRUCTIONS AFTER AMNIOCENTESIS — after the amniotic fluid has been taken you should avoid the following:
Travelling for several hours immediately after the procedure.
Work for 48 hours. You do not need to stay lying down during this time, but it is best to stay at home and avoid any strenuous activity. Moving around the house and light tasks (preparing food, for example) are allowed.
Sexual intercourse for about 20 days.
In the first day or two after the amniocentesis you may see a spot of blood on your underwear. This should not worry you. You should, however, contact your doctor in the following situations:
If you see: large amounts of fresh blood
If you see: large amounts of fluid from the vagina
If you have severe pain in the lower abdomen.
If you develop a fever.
For the 4 days after the test you should take the following medication:
CECLOR 750 mg capsules (one capsule every 12 hours)
If you are Rhesus negative you will need an intramuscular injection of Rhophylac within 48 hours, which you will also obtain from the pharmacy.