Amniocentesis is a prenatal diagnostic test in which a small amount of fluid is removed from the amniotic sac surrounding the fetus and sent for testing. This test is used to diagnose any prenatal chromosomal, genetic abnormalities in the fetus and fetal infections. It is usually performed between 16 and 20 weeks of pregnancy. This test is primarily for those expecting mothers who are at increased risk for genetic and chromosomal problems.  

Why is this procedure done?

  • When the first trimester or second trimester screening shows a ‘high risk’ for chromosomal disorders 
  • When there is a high suspicion for Down syndrome on the second trimester ultrasound 
  • When an abnormality is detected in the baby at the anomaly scan
  • To rule out certain genetic disorders
  • To confirm fetal infection when the mother is suspected to have certain infections, like rubella, CMV, toxoplasma, etc or there are signs of fetal infection on the scan

How is it done?

Amniocentesis is done by passing a thin needle through the mother’s abdomen into the uterine cavity under continuous ultrasound guidance to obtain a small amount of amniotic fluid from around the baby. The test is done under continuous ultrasound guidance so that the needle avoids both the baby as well as the placenta. 

This test is usually done between 15 to 18 weeks of pregnancy; however it may be done anytime afterwards when indicated. The amniotic fluid sample is then sent to the laboratory for analysis. For some tests maternal blood sample might also be required.

How painful is the procedure? Will anaesthesia be given to me?

Most of the procedure is most often uncomfortable or painful as routine blood sampling. Local anaesthesia is almost never needed for amniocentesis.

What are the risks associated with it?

There is small risk of miscarriage of around 1 in 300 associated with amniocentesis. Although all precautions are taken during the procedure to minimize infection, there remains a small risk of infection (1 in 1000). In about 1 in 100 patients, the culture may fail and the full karyotype may be unavailable.

What should I expect before the procedure?

The doctor will explain the procedure, why it should be done and the associated risks as outlined above. You will be asked to sign an informed consent. Your blood group and certain other blood tests (HIV, Hepatitis B) will be checked.

What should I expect before the procedure?

You will be asked to rest in the department and the baby’s heart beat will be checked after half an hour. There is no restriction to your daily activities though the doctor may advice you to stay home for 3 days to minimize chances of infection. You may have slight bruising at the site of needle entry. You may also have some spotting or mild cramping for a couple of hours. If you have fever, vaginal bleeding or leaking or contractions, you must report to the hospital.

How long do the results take to come?

The FISH report comes within one week and the full the karyotype report takes 2 to 3 weeks. The timing of other results will depend on the test performed and usually varies between 7 to 10 working days