Amniocentèse

The amniocentèse is a medical procedure used for a Prenatal diagnosis, in which an minor amount of Amniotic liquid is extracted from the amniotic cavity (Amnios is one of the three envelopes of egg) in which is the Fœtus.

The amniocentèse can be practiced as soon as there is enough amniotic liquid surrounding the fetus and that a sample can be taken with a minimum of risk, i.e. between the fourteenth and the twentieth week of Aménorrhée. It forms part with the biopsy of trophoblaste (Choriocentèse) and the puncture of fetal blood (cordocentèse) of the invasive means of Prenatal diagnosis.

The amniocentèse allows:

to establish the Chromosomic chart standard fetus,
to seek certain fetal infections (Toxoplasmose, Cytomegalovirus), or anomalies chromosomal and hereditary diseases.

She is proposed to the expectant mothers systematically approaching or exceeding forty (when the risk of trisomy is greatest), like in a certain number of cases more targeted like suspicion of anomaly chromosomal or the fetal suspicion of infection.

Risks

In the expectant mothers carrying the virus of the AIDS or Hepatitis B, a amniocentèse risk to transmit this disease to the fetus.

The amniocentèse is a little less risky for the fetus than the catch of a sample of trophoblase (Biopsie of trophoblaste), but the latter can be realized earlier.

The risks of the amniocentèse are

the Avortement (Risk of 1%): A study carried out in 2007, seems to indicate that the additional risk of miscarriage in the event of amniocentèse is about 1/400, thus not raising the risk of miscarriage total which is about 1/200 (0,46 to 0,53%)
the escape of amniotic liquid
the premature rupture of the membranes
fetal death In utero

The risk of loss of the pregnancy is evaluated between 0,3 and 0,5% in the statistics of 2004, against nearly 25% in the statistics of 1975.

Procedure

The amniotic liquid is obtained by using long a Aiguille assembled on a syringe and guided by ultrasound S and passing through the Abdomen of the mother. The taking away does not require most of the time a local Anesthésie and does not make more badly than a simple puncture. The quantity of amniotic liquid is of 20 ml to carry out a chromosomic chart. If the woman is Groupe negative Rhesus, it is necessary to manage with this one of the Gamma-globulines anti-D to prevent a Iso-immunisation rhesus responsible for the haemolytic Maladie of the newborn to the birth.

Result

The result of a chromosomic chart per study of the amniotic liquid is long (3 to 4 weeks) because it is necessary that the cells multiply (cellular culture) to be able to individualize the Chromosome S. It exists a technique (Fluorescent In situ Hybridization, F.I.S.H) which makes it possible to give the result in a few hours, but only for the Trisomie S 21,13,18 and for other anomalies concerning the sexual chromosomes. The cellular culture must however be carried out to confirm the result. According to the Center Mother Children of Quebec in 2004, since this technique F.I.S.H is available one makes much less puncture of cord to obtain fetal blood. Always in Quebec, a F.I.S.H increases the cost of approximately 300 Canadian dollars.

Tests

Its principal goal is the chromosomic chart of the fetus, in other words the chart of its chromosomes to detect the anomalies of the chromosomic chart such as for example the Trisomie 21 (mongolism or syndrome of Down). One puts in culture his cells in order to look them under the microscope. One also measures the concentration of Alpha-fœtoprotéine which is a neurological marker of anomaly like the Spina bifida.

An investigation is in hand in all the France, in order to check so by combining the various methods of diagnosis of trisomy 21, such as the measurement of clearness nucale, the proportioning of the serum blood markers, the age and the family history of the mother, one could currently lower up to 5% against 11% the rate of necessary amniocentèse.

Criteria to make a amniocentèse

The amniocentèse which can be dangerous for the fetus, there exist criteria to choose when one decides to make a amniocentèse:

the old one of the mother is higher than 38 years
There were antecedents in the phratry, those possibly being able to repeat itself for the child to be born either by the chance, or by a problem in the Méiose which repeats
One of the parents has a mosaic of cells carrying an anomaly even if its chromosomic chart is normal
One of the relative carrying anomaly of the chromosomes is balanced:

translocation robertsonnienne balanced
balanced reciprocal translocation
inversion perished or paracentric
anomaly of the Gonosome S: XXX or XYY
more one creates low imbalances in the meiosis, plus the child to be born will be viable

sign of echographic call: malformation of the bodies (of the heart, kidneys etc…), high clearness nucale, quantity of amniotic liquid, delay of growth
presence of a serum marker

See too

Choriocentèse

Random links: