What is Amniocentesis?

Amniocentesis involves examining the cells in the fluid surrounding the fetus (amniotic fluid). The cells in the amniotic fluid are derived from the fetus and so the chromosomes present in these cells are the same as those of the fetus. As a result, we can check if your baby has any genetic or chromosomal abnormalities.

When is amniocentesis offered?

Amniocentesis is not available to all pregnant women. It is only offered if your baby is more likely to have a genetic disorder.

How is amniocentesis performed?

Amniocentesis usually takes place between the 17th and 23rd week of pregnancy, but you can perform it later if necessary. It may take place earlier, but this can increase the risk of complications of amniocentesis and is usually avoided.

An antiseptic solution will first be used to on the skin of your abdomen to minimize the risk of infection.

A long thin needle is then inserted through the mother's abdominal wall under ultrasound guidance. The needle passes through the amniotic sac that surrounds the fetus and a small amount of amniotic fluid is sucked and sent for analysis.

The fluid is the urine of the fetus and the amount removed by amniocentesis is accumulated within a few hours.

The procedure takes 1 minute and then the fetal heart rate is checked.

In about 6 out of every 100 women undergoing amniocentesis, there is difficulty in getting enough fluid, so the needle must be inserted a second time. This is usually due to the baby's position or if the amniocentesis is performed later than 28 weeks of gestation. If the second attempt is also unsuccessful, you will be offered another appointment.

What should I expect after amniocentesis?

For the first two days there may be some discomfort in the abdomen, light bleeding or abdominal pain that may be like period pain. Simple painkillers such as paracetamol can be taken.

If you have severe abdominal pain, vaginal bleeding, loss of fluid in your vagina, or if you develop fever, chills, seek medical advice from your attending physician or the on-call hospital.

What diseases can amniocentesis identify?

• Down Syndrome (Trisomy 21) - all children born with Down Syndrome have some degree of learning disability and mental retardation, but this varies considerably among children.
• Edwards Syndrome and Patau Syndrome - condtions that can lead to miscarriage, mortality or severe learning disabilities. These pregnancies are rarely come to a delivery.
• Thalassemia - (a condition that affects the red blood cells, which can cause anemia, restricted grawth and organ damage).
• Sickle cell disease - (erythrocytes develop abnormally and are unable to properly transmit oxygen around the body).
• Cystic fibrosis - a condition where the lungs and gastrointestinal system produce and are blocked by a thick sticky mucus.
• Phenylketonuria - (your body cannot break down a substance called phenylalanine, which can reach dangerous levels in the brain).
• Duchenne muscular dystrophy - (a condition that causes progressive muscle weakness and disability).
• Many other genetic syndromes. (e.g. skeletal dysplasias)

When can I expect the results?

Results for Down Syndrome (Trisomy 21) and other major chromosomal abnormalities are usually available within three days. If we want to investigate rare genetic abnormalities or suspected syndromes it can take up to 3 weeks to get definitive results. Once we receive the results, we will invite you to in order to have a detailed discussion.

Unfortunately, there is no cure for most of the diseases diagnosed by amniocentesis, so you should carefully consider your options.

You may decide to continue your pregnancy by collecting information about the condition so that you are fully prepared. Learn more about having a baby that can be born with a genetic disorder and if needed you will be able to get specialist advice from a clinical geneticist.

What are the risks associated with amniocentesis?

The risk of miscarriage due to amniocentesis is about 0.3-0.5% and this is the same as the risk of chorion villus sampling. If the test is performed after 24 weeks of gestation then there is a 0.5-1% chance of preterm delivery. If a miscarriage is to occur as a result of the examination, this will occur within the next three days.

The risk of miscarriage is greater when pregnancy is less than 17 weeks (2-3%).

Some studies have shown that when amniocentesis is performed before 17 weeks, there is little risk for the baby to develop talipes (clubfoot). To avoid this risk, we do not have amniocentesis before 17 weeks.

Amniocentesis usually takes about 2 minutes, 10 minutes to prepare although counselling may take about 30 minutes.

Amniocentesis is usually described as unpleasant and not painful. Some women describe experiencing pain similar to period pain or feel pressure when the needle comes out.

infection

As with all types of surgery, there is a risk of infection during or after amniocentesis. However, serious infection occurs in less than 1 in every 1,000 cases.

Rhesus sensitisation

If your blood type is Rhesus (RhD) negative but the fetal blood type is RhD positive, sensitisation may occur after amniocentesis.

This is because even a small amount of fetal blood enters the mother's bloodstream and your body begins to produce antibodies, which if untreated, can cause the fetus to self-damage its red blood cells. If you do not already know your blood type and Rhesus, you should have a blood test in order to know this information before having your amniocentesis to see if there is a risk of sensitisation. If necessary, an anti-D immunoglobulin dose may be administered to avoid sensitisation.