Amniocentesis

Published by Sarah Horrocks
Published on 29 April 2008

During your pregnancy your doctor may offer you an amniocentesis. What is it? Does it indicate abnormalities for the baby? Here's what you need to know.

What is it?
Amniocentesis is a test that takes a sample of amniotic fluid (surrounding the baby in the uterus).

Why is it done?
It provides information about the baby’s health and development. It allows healthcare professionals to count chromosomes to determine if there is:
- a risk of chromosomal abnormalities that can cause genetic disorders linked to the sex of the baby
- a risk of Down's syndrome
- a risk of hereditary disorders
- a risk of malformation of the central nervous system

What happens?

The doctor will insert a long, thin, hollow needle into the abdominal wall and into the sac of fluid around the baby. Ultrasound is used to pinpoint a pocket of amniotic fluid a safe distance from the baby and placenta, and to guide the insertion of the needle. The test lasts about 20 minutes.

Information

You will receive all the information you need from a doctor before the procedure. Don’t be afraid to ask questions: the healthcare team will be specially trained to deal with worried future parents.

Does it hurt?

No more than a blood test, hence no anaesthestic is required.

When?

It is carried out from the 16th week of pregnancy and sometimes as late as the 3rd trimester if there are concerns about the baby’s health. A blood test is taken first to check the levels of certain hormones that can reveal a trisomy.

What are the risks?

Amniocentesis is a surgical intervention and as such presents certain risks. There is a low percentage risk of infection, miscarriage and inability to analyse the fluid (as there may be traces of blood in the sample). However, to prevent miscarriage you will be given a shot of Rh immunoglobulin after the procedure. You will need to lie down for the rest of the day.

Who is it offered to?

All future mums over the age of 35 may be offered the option of the test after being given the informed choice (because risk of trisomy increases with age) but also in case of a risk of hereditary disorders or if there is Down's syndrome in the family.

When do you get the results?

You need to wait up to two weeks before you get the full results.

What if there is a problem?

You will be offered genetic counselling so that you can get more information and discuss your options. If it’s a serious abnormality then you may be offered a therapeutic termination after discussing it with a counsellor and doctor.