Trisomy 21: how is an amniocentesis performed?


Amniocentesis is a prenatal screening test that involves taking a small amount of amniotic fluid, which bathes the fetus during pregnancy. “The amniotic fluid collected contains fetal cells analyzed in the laboratory”, specifies the site of the Health insurance. The objective is to detect any genetic or chromosomal abnormalities before the birth of the child.

This examination may be offered for different reasons. The main ones being:

In concrete terms, such screening makes it possible to estimate the risk that the unborn child will be affected by a congenital chromosomal abnormality, such as trisomy 21; of one genetic disease, such as cystic fibrosis or fragile X syndrome; or even a malformation.

Several factors may lead your gynecologist or midwife to recommend that you have an amniocentesis. According to an explanatory guide from the Center hospitalier de l’Université de Montréal, this screening test is mainly offered in the following cases:

Amniocentesis can be performed from the fifteenth week of pregnancy. It is usually scheduled during the third month, but can nevertheless be carried out until the end of pregnancy if necessary.

Insofar as this medical examination is not trivial, the risk of trisomy 21 must be evaluated beforehand before carrying out an amniocentesis. To do this, a combined screening is offered to each pregnant woman during the first trimester of pregnancy. This goes through a blood test for serum markers (PAPP-A, ß-HCG) and a nuchal translucency measurement of the fetus by ultrasound.

Taking into account the results of these two examinations, but also mother’s agedoctors will be able to assess the risk of trisomy 21. ”, indicates the site of the High Authority of Health.

On the other hand, “for women with a risk greater than 1/50 as for women at high risk due to increased nuchal translucency (≥ 3.5 mm), the HAS recommends offering a fetal karyotype from the outset”.

Amniocentesis: what are the risks?

Invasive screening, amniocentesis presents two main risks:

  • a risk of miscarriage, estimated at 1 case out of 300;
  • a very rare risk of infection of the uterus.

Be reassured however: you will have, before this examination, a scheduled interview with the obstetrician-gynecologist who should do it. You can then ask him all your questions, in order to make an informed choice. This meeting is an opportunity to discuss the possibility that your child has a serious illness or a congenital anomaly, other possible screening solutions, existing treatments, medical support for children with disabilities, the advantages and disadvantages. amniocentesis, etc.

During this exchange, reminds you that it is important to inform your doctor about:

  • your health status ;
  • your possible treatments in progress;
  • your family medical history (diseases, disabilities, etc.) and personal (such as a miscarriage during a previous pregnancy).

“If you are HIV positive and not treated with antivirals, there are a minimal risk of contamination of your child during amniocentesis”, specifies the site of the Health insurance. The practitioner will therefore prescribe an antiviral treatment for prevention.

At the end of the interview, the doctor will ask for your agreement to carry out the amniocentesis and, if necessary, will have you sign a consent form (mandatory to take the sample) and will schedule the appointment. Note however that nothing obliges you to practice this examination, it is your decision; hence the importance of having obtained all the answers to your questions beforehand.

How is amniocentesis performed?

On D-Day, before leaving for your exam, it is recommended that you take a shower and soap your stomach well. However, you do not need to be fasting for this test. Don’t forget to bring some documents: vital card, mutual insurance card, blood group card and doctor’s prescription. If you have fever or uterine contractions or blood loss, contact the establishment where you have an appointment: a postponement of the amniocentesis may be recommended.

Once there, in the examination room, you lie on your back, your shirt pulled up to free your abdomen. The doctor (a gynecologist-obstetrician) begins by performing a ultrasound, to visualize the placenta, amniotic fluid and fetus. It disinfects your lower abdomen and, while guiding itself with the ultrasound, insert a long, very thin needle. So, he collect 15 to 30 ml of amniotic fluid in a syringe, which represents a maximum of 10% of the total volume of this liquid. Rest assured, the latter is quickly renewed by the body and will be replaced in 5 or 6 hours.

The removal is very quick and painless, although it may cause a discomfort, even a feeling of abdominal cramp. Throughout the collection, then at its end, the doctor checks that the fetus is well, always using ultrasound. In total, the examination as a whole rarely lasts more than 10 minutes.

Precautions to take after the examination

“After the amniocentesis, you stay a few minutes under medical supervision, then you can go home,” explains the Health Insurance website. It is best to come to the exam by car and have someone accompany you so that you can be driven home. Without necessarily remaining bedridden, it is better rest the rest of the day and take 24 hours off before returning to work. The following days, avoid overworking yourself.

During the hours following the collection, “you may feel a pulling or painful sensation, where the needle was inserted. These phenomena are not serious”, specifies On the other hand, if you have fever, uterine contractions, loss of blood or amniotic fluid, or abdominal pain following the examination, you must consult urgently.

Amniocentesis: when will I receive the results?

The time required to obtain results varies according to the type of analyzes carried out. For example, the results of the search for chromosomal abnormalities for trisomy 21 are generally available in three days. In contrast, a full karyotype analysis may take two to three weeks.

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