All about amniocentesis

What is an amniocentesis?

Amniocentesis is most often prescribed in cases where the fetus is at high risk for chromosomal abnormalities, or may be the carrier of an inherited disease. It can also reassure the baby’s health. It is a prenatal examination which can be distressing for the future parents… An amniocentesis can be indicated in various situations.

If there is a significant risk that the child presents a chromosomal abnormality mainly a trisomy 13, 18 or 21. Previously, amniocentesis was systematically performed on pregnant women over 38 years. But 70% of children with Down’s syndrome are born to mothers under the age of 21. Now, whatever the age of the mother-to-be, a risk assessment is carried out. Beyond a certain threshold, amniocentesis is prescribed if the mother wishes.

Can we refuse an amniocentesis?

You can refuse an amniocentesis, of course! It’s our pregnancy! The medical team gives an opinion, but the final decision rests with us (and our companion). Moreover, before doing an amniocentesis, our doctor is required to inform us about the reasons for which he offers us this examination, what he is looking for, how the amniocentesis will take place and its possible constraints and consequences. After answering all our questions, he will ask us to sign an informed consent form (required by law), essential to be able to send the samples to the laboratory.

Evaluating the risks of chromosomal abnormalities in children

Three parameters are taken into account:

The size of the neck of the fetus (measured at1st trimester ultrasound, between 11 and 14 weeks of amenorrhea): it is a warning sign if it is greater than 3 mm;

The assay of two serum markers (carried out from an assay of hormones secreted by the placenta and passed into the mother’s blood): an abnormality in the assay of these markers increases the risk of having a child with Down’s syndrome;

Mother’s age.

Doctors combine these three factors to determine the overall risk. If the rate is greater than 1/250, an amniocentesis is advised.

If there is a child in the family with a genetic disease including cystic fibrosis, and both parents are carriers of the deficient gene. In one in four cases, the fetus is at risk of carrying this pathology. 

If a malformation is found on ultrasound, regardless of the time of pregnancy

To monitor the progress of high-risk pregnancies (eg, rh incompatibility, or assessment of lung maturity).

Amniocentesis can take place from the 15th week of amenorrhea until the day before childbirth. When prescribed because there is already a strong suspicion of chromosomal or genetic abnormality, it is performed as soon as possible, between the 15th and 18th week of amenorrhea. Before, there is not enough amniotic fluid for a proper examination and the risk of complications is greater. Therapeutic abortion is then always possible.

How does amniocentesis take place?

Amniocentesis takes place during an ultrasound, in a hospital, in a sterile environment. The mother-to-be does not need to be fasting and the sample does not require any anesthesia. The puncture itself is no more painful than a blood test. The only precaution: if the woman is rhesus negative, she will have an injection of anti-rhesus (or anti-D) serum to avoid blood incompatibility with her future child (in case he is rhesus positive). The nurse begins by disinfecting the belly of the mother-to-be. Then, the obstetrician precisely locates the position of the child, then introduces a very fine needle through the abdominal wall, below the umbilicus (navel). He draws up a small amount of amniotic fluid with a syringe and then injects it into a sterile vial.

And after amniocentesis?

The mother-to-be returns home quickly with a few specific instructions: stay at rest all day and above all, go to the emergency room if bleeding, fluid discharge or pain appear in the hours and days following the examination. The lab communicates the results to the doctor about three weeks later. On the other hand, if the gynecologist only asked for very targeted research on a single anomaly, trisomy 21 for example, the results are much faster: around twenty-four hours.

Is the amniocentesis reimbursed by Social Security?

Amniocentesis is fully covered, after prior agreement, for all future mothers who present a particular risk: women 38 years and over, but also those with a family or personal history of genetic diseases, a risk of Down’s syndrome. 21 fetal equal to or greater than 1/250 and when the ultrasound suggests an abnormality.

Soon a generalized blood test for expectant mothers?