An amniocentesis is a medical procedure performed to sample the fluid around the baby in the uterus (womb). This fluid is collected using a needle inserted through the pregnant woman’s abdomen.
The most common reason for having an amniocentesis is to test for Down syndrome or other chromosome (or genetic) conditions. This test is often offered because of a suspected chromosome or genetic condition found on ultrasound, or by a prior screening test.
Sometimes a woman may have an amniocentesis to test the baby for other conditions such as an inherited disease, blood group, or an infection.
Your doctor should fully explain the reasons for offering an amniocentesis to you and obtain your written consent before performing the procedure.
How is amniocentesis performed?
An amniocentesis is a procedure performed by a specialist doctor using ultrasound assistance. You do not need a full bladder or any special preparation before the procedure. You can eat and drink normally on the day.
After checking the baby’s position and heartbeat with the ultrasound, the doctor cleans the skin of your abdomen with antiseptic. Ultrasound is used to guide the amniocentesis needle safely through the skin into a pocket of fluid inside the uterus, avoiding any needle contact with the baby.
Usually, about 1-2 tablespoons (15-30ml) of fluid is drawn up through the needle into a syringe and then transferred into a tube for laboratory testing. The needle only stays inside the uterus for a few minutes.
There is no anaesthetic required and you will remain awake during the whole procedure. Afterwards a small dressing is placed on the skin needle puncture site. You may find it helpful to bring a support person with you for the procedure.
Does it hurt?
The pain from an amniocentesis needle is similar to having a blood test from your arm, but there can be cramping or period-like pain during the procedure as well. The vast majority of women cope with an amniocentesis without any special medication for pain relief.
What are the risks?
There is a small risk of miscarriage during any pregnancy and having an amniocentesis may slightly increase the overall risk of miscarriage. The risk of miscarriage due to amniocentesis is estimated to be less than 1 in 200 (< 0.5%).
The usual amount of fluid removed at amniocentesis (15-30ml) is small and its removal will not affect the development of the baby if performed after 15 weeks.
Are there any test results that need to be checked before I have an amniocentesis?
It is important to confirm how far your pregnancy has progressed (your gestational age) before your amniocentesis is booked. It is not recommended to have an amniocentesis before 15 weeks gestation, as the risk of complications is higher.
Your blood group should also be known before having an amniocentesis. If you are a ‘negative’ blood group (Rhesus negative), then you will need to have an injection of anti-D immunoglobulin after the procedure.
Your hepatitis B and HIV status (and hepatitis C, if performed) should also be reviewed. All pregnant women are tested for these infections in early pregnancy, so the results should be readily available.
You should discuss your individual circumstances with your doctor if you are positive for any of these infections.
How should I look after myself after the procedure?
You should avoid any heavy physical activity after your procedure, but you do not need to rest in bed. You should feel physically back to normal by the next day and can resume your normal activities after 1-2 days. Your doctor should discuss what to expect following an amniocentesis. Some mild period-like pain is common on the first night, and it is safe to use a regular dose of paracetamol for pain relief.
When to get medical advice?
If you have any vaginal bleeding, severe abdominal pain, high fever or unusual fluid loss from the vagina, you should go to your emergency department. In general, if you have been well for the first week or two after the amniocentesis, it is unlikely that any complications will happen after this.
How do I get the results of the amniocentesis?
Please confirm with your doctor how you are going to get your results. You should be given a contact number to call in case you have any concerns.
This document is intended to be used as a guide of general nature, having regard to general circumstances. The information presented should not be relied on as a substitute for medical advice, independent judgement or proper assessment by a doctor, with consideration of the particular circumstances of each case and individual needs. This document reflects information available at the time of its preparation, but its currency should be determined having regard to other available information. RANZCOG disclaims all liability to users of the information provided.
© RANZCOG 28/07/2016
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