Prenatal diagnosis is the set of resources used for early detection of diseases or malformations of the fetus. . It involves any diagnostic procedure performed in order to predict or determine the status of the child before its birth. It therefore aims to detect a fetal abnormality and to clarify the diagnosis and prognosis. It is important to note at the outset the difference between prenatal diagnosis and screening, often confused notions: while prenatal screening detects mainly a risk factor for disability (trisomy 21, for example), prenatal diagnosis allows meanwhile to establish or exclude with certainty the presence of an anomaly. Usually the diagnosis is made following a positive screening.Thus, the serum markers is a method of detecting pregnancy as "high risk" and not a method of diagnosis of trisomy 21.
Before 1972, there were no techniques to achieve a genuine prenatal diagnosis. This situation has changed dramatically since that date with amniocentesis (aspiration of amniotic fluid in order to study its characteristics), then with ultrasound in 1974. It was the appearance of imaging and obstetric techniques to perform fetal sampling. Since then, other techniques have emerged.Now, the ultrasound has entered a phase of actual testing for pregnancies without particular risks or clinical abnormalities. If for a long time now there has been is a compulsory medical surveillance of pregnancy, now couples demand more that is to say a child without disability or abnormality. Now pregnant women are amenable to prenatal examinations, whose number has grown steadily. Prenatal diagnosis is therefore built into the logic of mandatory monitoring of pregnancies and beyond the traditional public health policy, namely the protection of motherhood. Our society acceptsless and less disability whatever its intensity. The proof is in the repetitive abuse in recent years, ultrasound during pregnancy and in the development of applications for amniocentesis. Techniques : There are different techniques involved at different stages of pregnancy. We distinguish between non-invasive (no risk to mother and child). And invasive (said of a technique to get inside the body) is not devoid of risk to mother and child.
Non-invasive techniques :
-Ultrasound: :An ultrasound probe placed on the belly of the mother sends ultrasounds that meet the anatomical structures of the fetus. The recovery of ultrasound allows us to reconstruct a synthetic image of the fetus to observe its development. Additionally it can find morphological abnormalities such as limb or organ anomalies , and also some tumors. It also allows an accurate determination of gestational age and control the proper development of the unborn child. Ultrasound is now indispensable and mandatory in the monitoring and prenatal diagnosis. 60% of IMG are decided secondarily to an ultrasound examination. -The embryoscopie or fetoscopy:-Technical development: This involves introducing , through the cervix, an optical system to observe the embryo in its amniotic sac. This technique is designed primarily to detect inherited defects of the skull, limbs, skin and also cleft lip and palate, in a context of history.It also allows some fetal surgeries.Determination of serum markers in maternal blood: This technique is commonly called the TRIPLE TEST.It is performed between the 15th and 18th week of pregnancy. This is a blood test that measures the 3 molecules : the hormone chorionic gonadotropin (HCG), alpha-fetoprotein (AFP) and unconjugated estriol (E3) These substances are characteristic of pregnancy and their rates differ when the fetus suffers from Down syndrome or spina bifida. The calculated risk for the pregnancy of the patient is interpreted relative to the threshold of 1 / 250 at the time of sampling (by ministerial decree of 23 January 1997): :-if this risk is lower, the patient is classified in a non risk group which does not normally justify the risk of doing an amniocentesis, -if this risk is greater than or equal to 1 / 250, an amniocentesis will be offered to the couple after verification of clinical information and ultrasound data. However, a positive test does not necessarily mean that the child is suffering, but simply that the probability is higher. This means that 5% of pregnant women are liable to have an amniocentesis . We should inform the patient that serum markers do not establish a diagnosis but only assess risks with a specificity that is far from satisfactory.
Invasive techniques :
3 techniques exist depending on the progress of the pregnancy::-the chorionic villus sampling when the pregnancy is between the 10th and 11 th week. It involves removing the chorionic villi. The chorionic villi are small outgrowths developing from the membrane surrounding the embryo and are subsequently the placenta. After an ultrasound detecting villi a tube is inserted through the cervix to the placenta and the villi. The doctor performs the removal of some villi. These provide recovery of embryonic DNA, to perform a karyotype and to look for chromosomal abnormalities. In 1% of cases, miscarriage can occur within one week after the examination. -amniocentesis between 11 th and 15 th week. It is done under local anesthesia and involves removing, using a thin needle guided by ultrasound, amniotic fluid. The fetal cells which are retrieved are used to establish a fetal karyotype and search for chromosomal abnormalities. This technique is routinely offered to women over 38 years old or women whose pregnancy is considered at risk by the presence of family history, or because of triple test and ultrasound have shown an anomaly. This aspiration is a simple examination but the risk of accidental interruption of pregnancy is not negligible. -lCordocentesis is from the 21 st week. It is a fetal blood sampling performed on the fetus by puncturing the umbilical cord vein. It allows the realization of the karyotype on fetal cells. Since 1983, fetal blood sampling has become a complementary method of examination which has paved the way for genuine fetal medical diagnosis and therapy. Being late,on in the pregnancy it is obviously not without risk to the fetus. The risk of fetal loss is about 2%. It allows the diagnosis of a number of diseases, including skin, hemoglobin or even of rubella or toxoplasmosis. .
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Victor Hugo