Amniocentesis
Amniocentesis is an invasive form of prenatal diagnosis.
This method involves the removal, by means of a puncture, of a small amount of amniotic fluid (the so-called "waters" that surround the fetus in the uterus during pregnancy), crossing the woman's abdomen and the amniotic sac (or amnios) ), or the membrane surrounding the fetus.
This operation must be performed by an expert gynecologist using an ultrasound check.
Amniocentesis occurs between the 15th and 20th week of gestation, when the amniotic cavity has reached sufficient size for the practice to not pose a danger to the fetus; as in the case of villocentesis this procedure is entrusted to the expert doctor and is associated with a risk of abortion between 0.5 and 1%.
The analysis of the cells present in the amniotic fluid allows to evaluate the fetal chromosomal structure (analysis of the karyotype) and the fetal DNA; the level of accuracy and diagnostic value of the examination depend on the type of genetic investigation that is decided to take.
The indications for the execution of the amniocentesis are the same as for the villocentesis:
- Maternal age over 35 years
- Presence of chromosomal alterations in parents
- Family history of genetic diseases
- Chromosomal alterations detected in previous pregnancies
- Fetal malformations detected on the ultrasound examination
- Positive result of the exams made with non-invasive methods (Eg: Combined Test)
In addition to these situations, amniocentesis is recommended in cases where the previously performed villocentesis has shown a contamination of the sample with maternal origin tissue which makes interpretation of the results difficult.
CVS
Villocentesis is the earliest form of invasive prenatal diagnosis: the examination is performed between the 10th and 12th week of gestation.
The villocentesis consists in the collection, by the abdominal or vaginal-cervical route, of a small amount of chorionic villi (microscopic ramifications that form the outermost part of the placenta).
The chorion sample is aspirated under continuous ultrasound guidance, with a needle penetrated through the abdominal and uterine wall, until reaching the trophoblast (the precursor tissue of the placenta where the chorionic villi are located).
It is an invasive technique, associated with a percentage of abortion risk estimated at around 0.5-1% and which is related to the manual skills and experience of the operator.
The biological sample taken is genetically relevant to the fetus; the subsequent analysis makes it possible to unequivocally determine the presence of a broad spectrum of chromosomopathies or other diseases of genetic origin.
The analysis of the cells and the DNA of the chorionic villi allows to evaluate the fetal chromosomal structure (analysis of the karyotype) and the fetal DNA (genetic and biomolecular analysis); the level of accuracy and the diagnostic value of the examination depend on the type of investigation that you decide to undertake.
Villocentesis is proposed to women judged to be at high risk for chromosomal abnormalities.
The indications for the execution of the villocentesis are the same as those of the amniocentesis, in particular:
- Maternal age over 35 years
- Presence of chromosomal alterations in parents
- Family history of genetic diseases
- Chromosomal alterations detected in previous pregnancies
- Fetal malformations detected on the ultrasound examination
- Positive result of the exams made with non-invasive methods (Eg: Combined Test)
Genetic Analysis
Amniocentesis and villocentesis describe two different sampling techniques of fetal origin on which genetic analyzes will be performed that have three different levels of accuracy:
- Traditional karyotype: performs the analysis of the chromosome structure of the fetus (karyotype) in relation to a panel of chromosome anomalies quite simplified (trisomy of chromosome 21 or Down syndrome, trisomies of chromosomes 13 and 18, monosomy of the X chromosome or Syndrome of Turner), which represent the most frequent pathologies.
- Molecular karyotype: it is a high-resolution examination of the fetal karyotype, which identifies not only the macroscopic alterations highlighted with the traditional karyotype (alterations in the number or shape of the chromosomes), but also some small size alterations (microdelections and chromosomal microduplications) . It also allows screening on more than 80 non-detectable chromosomal pathologies with traditional amniocentesis (Angelman syndrome, Cri-du-chat disease, Williams syndrome, Prader-Willi syndrome, etc.).
- Genetic analysis: not only the examination of the karyotype but also the analysis of fetal DNA, highlighting the mutations that are associated with the most serious and frequent genetic diseases (cystic fibrosis, X-fragile chromosome syndrome, congenital deafness, muscular dystrophy by Duchenne-Becker ...). It is usually performed in case of suspected diagnosis.
