What methods are used for fetal genetic material examination?

Chorion biopsy - chorionic villi sampling (CVS)

In early prenatal diagnostic of congenital disorders, chorionic villi sampling (CVS) has become very popular recently. In the essence of the idea that chorionic villi may be used in prenatal diagnostic is the fact that their chromosomal and genetic characteristics are identical to the fetal ones.

 

The main advantage of this method is in the fact that the fetal genetic material abnormality is detected as early as the first 12 weeks of the gestation, in a quick (up to 48 hours upon the intervention), and simple way, with practically equal risk for mother and fetus as with other methods. When identification of the genetic material abnormality is confirmed, the process of abortion is carried out in a simple way prior to 10th week of pregnancy. As determination of fetal karyotype identifies also the sex of the fetus, this intervention is recommended to the patients carrying the risk of transmitting the diseases related to sex chromosomes. Transabdominal approach is by far the most accepted method of chorionic villi sampling. The process is carried out with local anesthesia and is certainly most comfortable for the patients. The pregnant lies in a bed and the intervention is preceded by ultrasound examination for the purpose of estimation of vitality of the pregnancy and gestation age. By determination of the chorion frondosome position, the shortest way for insertion of aspirated needle is planned. Then, a needle (guiding needle with mandrel), is passed through the abdominal wall and uterine wall all up to the chorionic frondosome (amnion), and not disturbing the space of the embryo therewith, and then a certain quantity of chorionic villi for cytogenetic analysis is aspirated.

 

The whole procedure is carried out in the specialized hospital / polyclinic and immediately upon the intervention the patient may go back to usual activities. Within 48 hours upon intervention, at latest, the patient is informed about the results of the intervention.

Amniocentesis – amniotic fluid sampling(AC)

This method consists basically of sampling amniotic fluid wherefrom numerous elements may be analyzed.In the examination of the fetal genetic material, the intervention is, as a rule, planned in the pregnancy from 12 to 24 weeks.

Although modern ultrasound devices enable safe amniotic fluid sampling even in early pregnancy, the ideal time for intervention is the pregnancy period between 15 and 18 weeks. During this period number of fetal cells in the fluid of the fetus is satisfying and the ratio between vital and non-vital cells is optimum. In view of the pregnancy period during which the intervention is carried out in the literature it is known also as an early amniocentesis. Amniotic fluid may be sampled even after 24th week of pregnancy. This intervention is called a late amniocentesis and it is carried out for estimation the condition of the fetus (with Rh-aloimmunization for example), or for determination of the level of maturation (maturity) of fetal lungs and planning the date of delivery.

 

Ultrasound examination determines vitality of the fetus, estimates the gestation age, quantity of the fetal fluid and the position of amnion, and finally planned is the optimum path for passing the needle up to ‘pocket’ of the amniotic fluid wherefrom the sample is taken. Amniotic fluid is aspired by a syringe 15-20 ml, and forwarded for further testing (cytogenetic analysis).

Fetus blood sampling - cordocentesis (CC)

Cordocentesis (CC) includes transabdominal puncturing of umbilical cord of the fetus and fetus blood sampling. Due to its invasiveness and somehow higher risk involved therein, this intervention is as a rule carried out mainly in hospitals in patients with strong indications, and the pregnancy must be 20 weeks or higher. The patient is informed about the results of the intervention. a week after the intervention