Amniocentesis is an invasive procedure in prenatal diagnosis of chromosomal abnormalities and fetal infections, and also for sex determination, in which a small amount of amniotic fluid, which contains fetal tissues, is sampled from the amniotic sac surrounding a developing fetus, and then the fetal DNA is examined for genetic abnormalities. The most common reason to have an “amnio” is to determine whether a baby has certain genetic disorders or a chromosomal abnormality, such as Down syndrome.

It involves removing and testing a small sample of cells from amniotic fluid, which surrounds the fetus in the womb (uterus). It involves passing a thin needle into the uterus in order to remove a small amount of amniotic fluid.

Amniotic fluid contains cells that are normally shed from the fetus. Samples of these cells are obtained by withdrawing some amniotic fluid. The fluid is fetal urine and the amount removed by the amniocentesis re-accumulates within a few hours.

Amniocentesis is usually carried out between the 15th and 20th weeks of pregnancy, but may be performed later than this if necessary.

The Obstetrician usually asks the patient to come at 16 weeks for the test…WHY?



Doctors generally offer amniocentesis to women:

  1. That is 35 years old or older when they deliver
  2. Abnormal double test or triple test result
  3. With a previous pregnancy or a baby affected by a disorder such as Down syndrome, Aneuploidies, etc.
  4. Have a close relative with a disorder such as Down syndrome, Aneuploidies, etc.


Amniocentesis isn’t routinely offered to all pregnant women. It’s only offered if there’s a high risk your baby could have a genetic condition.

  1. Infection
  2. Injury to the baby
  3. Miscarriage – This is estimated to occur in 1% of women who have amniocentesis.

However, the test is typically done when a problem is suspected and the benefits outweigh the risks.