Amniocentesis (also referred to as amniotic fluid test or AFT) is a medical procedure used in prenatal diagnosis of chromosomal abnormalities. The doctor will pass a fine needle through your tummy to extract a small amount of amniotic fluid that surrounds the developing fetus. This sample of fluid will contain the fetal DNA that can be analysed in a laboratory. This is called genetic screening and can help diagnose abnormalities of the unborn baby. Prenatal diagnosis by genetic screening can detect Down syndrome, cystic fibrosis and other conditions caused by chromosomal abnormalities. It can also be used for prenatal paternity testing.
The laboratory analyses the fluid sample using a process called PCR (polymerase chain reaction.) It obtains a preliminary result of the testing for Down syndrome and a chromosome analysis in just 2 to 3 days. The rest of the specimen of fluid is then set up in a culture for karyotyping that usually produces an identical result to confirm the initial PCR after two weeks. Results from a full analysis for other chromosomal abnormalities can take up to two weeks.
You can have an amniocentesis performed at any time from 16 weeks of pregnancy. Before agreeing to the procedure, our consultant obstetrician will explain the risks and give you time to ask any questions. You will also need to sign a consent form. If you'd like to know the gender of your baby please tell the consultant during your appointment as we only report the gender on request. Please note that we will not perform an amniocentesis solely for the purposes of gender identification.
The procedure is usually very straightforward and is performed under continuous ultrasound vision to avoid any threat to your baby. Discomfort is minimal and the procedure only takes a minute or two. Most of the appointment time is taken up with preparation and counselling. Before our consultant performs the amniocentesis we need to know your blood group. If your blood type is rhesus negative you will need an injection of anti-D after the procedure is complete. You may hence need to attend for two appointments.
Whether or not you decide to have testing for Down syndrome or another prenatal diagnosis by amniocentesis, there will still be uncertainty. Amniocentesis cannot guarantee a healthy baby. It is a very personal decision, and no one can decide for you, but there is no right or wrong decision.
There is a 0.5 to 1% risk of miscarriage associated with having an amniocentesis. This means for every 200 procedures performed it is possible that 1 or 2 patients would experience a miscarriage and 199 or 198 pregnancies would progress normally.
Because an amniocentesis is performed later in pregnancy (when miscarriages are less likely to occur naturally) the risk may be lower than if you had a CVS (chorionic villus sampling) performed earlier in your pregnancy.
Consult your doctor if:
you have a family history of chromosomal abnormalities
your nuchal scan and blood testing for Down syndrome indicate a high level of risk
you wish to have an amniocentesis performed for your own peace of mind.
At Richmond Practice our consultant obstetricians offer prenatal diagnosis by amniocentesis as part of your private pregnancy care. We have sub-specialists in fetal-maternal medicine who are experienced in performing this procedure and we offer weekly clinics. Care is taken that you will feel comfortable and supported during the procedure.