Prenatal diagnosis is a branch that deals with the identification of structural or functional anomalies in the fetus.
Structural anomalies or malformations occur as a result of genetic defects. The second type of anomalies are deformations that occur in a genetically normal fetus, and are a consequence of a mechanical obstruction, for example, Limb contractures due to oligohydramnios (diminished around fruit water). Syndromes represent a set of multiple structural and / or functional anomalies. The genetic sonogram aims to detect such anomalies.
During the examination, strictly determined markers are measured which, depending on the association with a given syndrome, are divided into major and minor.
Major markers associated with trisomies 13, 18 and 21 are:
- Cystic hygroma
- Diaphragmatic hernia
- Atrium of the esophagus
- Duodenal atresia
Minor markers associated with Down syndrome are:
- Increased nuchal transplantation
- Nose bone abscess
- Hyperhocene focus in the heart
- Dilatation of the kidney structures
- Short femur (thigh bone)
- Short humerus (shoulder bone)
Down syndrome screening is performed in the first and second trimesters of pregnancy.
In the first trimester between 11 and 14 weeks, PRISCA is made taking into account ultrasonic markers such as nuchal translucency (NT), biparietal diameter (BPD), femoral length (FL) and the presence or absence of nasal bone NB), biochemical markers in the blood of the pregnant woman and using a program calculates the risk of this syndrome.
The sensitivity of the test is 79-97%, and false positive results are obtained in 5% of cases.
The same test serves for the detection of trisomy 13 and 18 with a sensitivity of up to 90% and false positive results in only 1%.
Risk factors associated with these syndromes:
- Female age > 35 y.
- Previous children with trisomy
- Early abortion anamnesis (<8 y)
Amniocentesis is indicated in high-risk women or in ultrasound signs of anomalies. It is an invasive procedure whereby using a needle and under the control of ultrasound, it enters the amniotic sac, and germination is taken, which is then sent to the genetic examination.
Depending on the gestational age of the fetus, amniocentesis is classified as:
- Early - between 11 and 14 y
- Late - between 11 and 14 y