Amniocentesis is one of the genetic tests that are most commonly carried out during pregnancy in order to determine whether there are chromosomal anomalies in the baby. It is a test that has a small risk of miscarriage, because it involves extracting a little bit of liquid from the amniotic sac. The results are reliable, as it is not a screening test.  

What is amniocentesis?

The objective of an amniocentesis is to obtain a small amount of amniotic fluid in order to take baby cells to analyze its chromosomes. The liquid is obtained by inserting a needle in the mother’s belly. This liquid usually contains some of the baby’s skin cells and when they are cultured, a kind of snapshot of these chromosomes is obtained.

By pairing off and observing chromosomes, you can find out if there is an extra chromosome that may cause an alteration in the baby’s development. For example, in Down’s syndrome –one of the most common anomalies- the baby has three chromosomes in the 21st pair, instead of just two. Amniocentesis can also check the genes, the smallest parts that chromosomes are composed of; to ensure that there is not a specific hereditary problem.

Although rare, it could happen that no cells are found in the extracted fluid, or that the culture is not successful. In this case the extraction must be done all over again. Amniocentesis is carried out between weeks 15 and 18 of pregnancy.

Reasons to undergo an amniocentesis

In general, amniocentesis is offered routinely to women over 35, because they are statistically at a higher risk of having a baby with a chromosomal alteration. Besides, it is also used in order to rule out any anomaly if the screening tests show the possibility of there being a problem. It is also used to locate the existence of hereditary genes that cause some illness such as hemophilia.

Currently there are very few illnesses that may be cured with the baby in uterus. What the amniocentesis results provide is information that may help the parents determine whether to go on with the pregnancy, and if so, what measures should be taken during delivery.  

Amniocentesis is an option that a pregnant woman may use or not. Some mothers decide they do not want to have this information at hand because they would have the baby anyway, and others prefer to undergo this test in order to rule out any possible option even when they are under 35 years old. 

How an amniocentesis is done

There is no special preparation required for this test, although you should take a few days off after having it done, in order to rest. This is because a small puncture is performed on the amniotic sac, and it must be given time to close. Plan to have your partner or a family member go with you, to feel more at ease.  

In order to carry out the test, you will be asked to lie down and expose your belly. They will disinfect the area where the needle will be inserted and you may be offered local anesthesia to avoid discomfort.

Before inserting the needle, the doctor will check which the best location is by means of an ultrasound. Don’t worry: he won’t prick your baby. Babies instinctively move away from it.

You may feel a slight prick, just like when you get a blood test, but that’s all. It isn’t a painful test. The doctor will guide the needle using the ultrasound, until it reaches the appropriate point, and will proceed to extract the amniotic fluid. He won’t extract much; only the equivalent of a couple of tablespoons. Then all you have to do is go home and be on bed rest for at least 24 hours, or 48 if you can. The results should be ready in a couple of weeks.  

After the test

There is a small risk of a miscarriage or an infection right after the test. For every 200 to 400 amniocentesis that are carried out, there is one miscarriage and one infection happens for every 1000 amniocentesis.

It could be normal to have a small leak of fluid after the test, but if the amount increases or doesn’t stop after a few hours, you should contact your doctor immediately.  

You should also call your doctor or go to the hospital if you feel painful contractions or if you are bleeding or have any symptom of preterm labor.