What is amniocentesis?
Amniocentesis is a test in which a small amount of fluid (amniotic fluid) is collected from the pregnancy sac around the baby in the womb. This fluid contains cells from the baby's skin and bladder which can be grown in the laboratory to test for chromosomal problems, like Down Syndrome, or DNA abnormalities, like cystic fibrosis.
Who may be offered amniocentesis?
Amniocentesis is always voluntary and only you can decide if you should have this test. The information below may help you decide whether or not to have this test.
The most common reason to have an amniocentesis is for those worried about the chances that the baby may have a chromosomal problem, like Down syndrome. This might include:
- Women with a First Trimester Screening (FTS) or Second Trimester Screening (STS) test suggesting an increased chance of having a baby with a problem
- Women who are anxious about the risk of problems, often because of their age
- Women who have had a previous pregnancy affected by a serious medical problem with the baby
How is amniocentesis performed?
Amniocentesis is performed from 15 weeks onwards. Ultrasound is used to carefully direct a very fine needle through the mother's abdomen, into the womb, and then into the amniotic fluid space around the baby, as shown in the picture.
A small amount of this amniotic fluid is then removed. The needle does not touch the baby. The fetal heart rate is checked both before and after the test.
Local anaesthetic is not usually used as the needle is so thin.
What preparation do I need before the test?
No special preparation is needed before the test. Your bladder does not need to be full. A scan is first performed to confirm the baby's size and the position of the placenta.
It is important to know what your blood group is before the test. If possible please ask you doctor or midwife to provide this information to you, or bring along your blood donor card. If you have a negative blood group you will also need to have a special injection of "anti-D" after the amniocentesis.
What should I expect after the amniocentesis?
For the first couple of days after the procedure you may experience some abdominal cramping, like period pains. This is relatively common and in the vast majority of cases is of no importance. You may find it helpful to take painkillers like paracetamol.
If there is a lot of pain or bleeding or if you develop a temperature please seek medical advice immediately from your obstetrician or midwife or from the Irish Maternal Fetal Foundation.
When can I expect my results?
The results for Down syndrome and other major chromosomal problems are usually available within 2 weeks. However, if you wish to get your results sooner than this, you can choose to have some of the amniotic fluid sample sent to a special laboratory that can provide some results in 2 to 3 days. The results for other special genetic conditions may take 2 weeks or longer. We will call you with your results as soon as they are available. We will also send a copy to your obstetrician, GP, or midwife.
What are the risks associated with the test?
The risk of miscarriage after amniocentesis is likely to be about 0.1% or 1 chance in 1000 or less. If a miscarriage is going to occur, you will usually have symptoms within the first 2 to 3 days after the test. Recent research from the RCSI Department of Obstetrics and Gynaecology has suggested that amniocentesis, when performed in expert hands, is probably much safer than previously thought. This recent study has suggested that the risk of miscarriage due to amniocentesis is less than 1 chance in 1,000.Fetal Anomaly Scan at 20 weeks to check for other abnormalities.