Amniocentesis Testing – What And Who Is It For?

Amniocentesis TestingIf you are pregnant or you have recently given birth, the chances are quite high that you have heard the word -amniocentesis . It is a hard-to-pronounce word but a very necessary procedure and owing to the fact that the risks are low for both mother and their unborn baby, it’s routinely recommended by obstetricians to women who are considered to be at a high risk for genetic diseases.

The soon-to-be mom who will be advised to undergo the prenatal test are those who have a family history of specific birth defects, and mothers who will be older than 35 years at the time of the delivery. The reason for recommending the test to women who are older than 35 is that, although it is possible for any woman (of any age) to have a baby with a chromosomal abnormality, the risk increases with the mother’s age.

The probability of carrying a baby with Down Syndrome increases from about 1 in 1,295 at age 20, to 1 in 82 at age 40. An amniocentesis will also be recommended to pregnant women who have a child with a birth defect or have been pregnant with a child who had a birth defect, or where an abnormality was detected by an ultrasound. In the case where the ultrasound was a determining factor for the test, the obstetrician was able to pick up a particular structural defect or defects commonly associated with a chromosomal problem.


The test

If an obstetrician suggests that an amniocentesis is performed, generally the procedure is carried out between the 15th and 18th week of pregnancy. The foetus is surrounded by amniotic fluid, a substance which is very similar to water. The fluid is made up of foetal skin cells that are shed naturally during the baby’s growth. Another substance found in the fluid is alpha-fetoprotein (AFP). AFP is able to provide vital information about the baby’s health and wellbeing while it is still in the uterus.

The test is a fairly simple one and involves a small amount of amniotic fluid being extracted from the sac that surrounds the foetus. A very small amount of fluid is removed. Perhaps the worst part of amniocentesis is the fact that a rather large, fine and sharp needle is used to remove the fluid. The needle is inserted into the woman’s uterus through the abdomen.

To prepare for the test, a small area of the woman’s abdomen is dabbed with antiseptic. To reduce discomfort, women may request a local anaesthetic. Using an ultrasound, the doctor will determine the position of the baby and placenta, and relying on ultrasound guidance, a thin, hollow needle is inserted into the abdomen and uterus, and finally into the amniotic sac. The needle is kept away from the baby keeping any risk to the unborn baby to a minimum.

An amniocentesis may also be done in the third trimester of the pregnancy and the results of this test will be used to determine if the baby’s lungs are mature enough for delivery. It will be performed on woman where there is a strong possibility of an early or a premature delivery. Furthermore the prenatal test may be used as an evaluation tool to ascertain if there is an infection in the amniotic fluid.

If you have been advised to undergo amniocentesis and you and your partner are eager to find out the sex of your baby, amniocentesis is the most accurate method to find out your baby’s gender before the birth.



During testing, it is not unusual for the woman to experience very minor cramping (similar to period pains). There is a very low risk that the testing could cause a miscarriage but the risk is less than 1%. Injury to the baby or injury to the mother is another small possibility as is the development of infection – yet again such risks are particularly uncommon.



The prenatal testing is not capable of detecting all birth defects, it’s used to successfully to detect the following conditions:

  • Down syndrome
  • Sickle cell disease
  • Cystic fibrosis
  • Muscular dystrophy
  • Tay-Sachs and related diseases

The amniocentesis will also be able to detect various neural tube defects which are diseases where the brain and spinal column do not develop correctly, like spina bifida and anencephaly. Taking into account that an obstetrician will rely on both results from the amniocentesis test and an ultrasound, other birth defects may also be detected (that may not be picked up by the prenatal testing). These birth defects are a cleft palate, a cleft lip, club foot, or certain heart defects. There are some defects that will not be detected by either the amniocentesis or the ultrasound.



The accuracy of amniocentesis is in the region of 99.4%. Inaccuracies may occur because of certain technical problems which may include the collecting of an insufficient amount of amniotic fluid or in cases where the collected cells do not grow when they are cultured.


Refusing the amniocentesis

A doctor will only recommend that a pregnant woman undergo the prenatal test, however the final decision rests with the mother (or the parents of the unborn child). A doctor will state his or her reason for recommending the testing, but will not force the mother to be tested. Once all the risks and benefits have been explained and weighed up by the expectant parents, the choice to undergo the testing is theirs!


The alternative to amniocentesis testing

Chorionic Villus Sampling (CVS) is an alternative prenatal test which is able to detect chromosomal abnormalities like Down syndrome, and many other genetic disorders. During this test, the doctor will remove cells from minute projections on the placenta which are known as chorionic villi and these samples are then sent to a lab for genetic analysis.

When it comes to the advantages offered by the differed testing procedures, one advantage is that CVS can be performed earlier than amniocentesis. In most cases the test can be done at the 11th of 12th week of pregnancy. The risks of a miscarriage after CVS is low – virtually the same risk factor as for amniocentesis. Over the years however, CVS has been linked to limb defects in babies, including the missing of fingers or toes, but this was more common when testing was done on women before their 10th week of pregnancy.


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