Invasive methods
The basic invasive prenatal diagnostic tests consist of puncture of the uterus to obtain amniotic fluid (amniocentesis), the removal of placentary tissue (chorion biopsy) or obtaining blood from the umbilical cord (umbilical blood sampling).
- 1
- Embryo
- 2
- Amniotic cavity
- 3
- Chorion cavity
- 4
- Uterine cavity
- 5
- Chorion frondosum
- A
- Amniocentesis
- B
- Chorion biopsy through the abdominal wall
- C
- Umbilical blood sampling (V. umbilicalis)
- D
- Transvaginal chorion biopsy
Illustration of the various possibilities for access to the embryo for diagnostic purposes.
Chorion biopsy
Chorion biopsy is an invasive diagnostic method that is mainly employed during early pregnancy (embryonic period). Normally, chorial tissue is removed trans-vaginally using a biopsy needle and examined in the direct preparation or after short-term in-vitro cultivation.
Amniocentesis
Amniocentesis represents an additional invasive prenatal diagnostic possibility. Here in the 13th – 15th WoP (15 - 17 weeks after the LMP) 10 - 20 ml of amniotic fluid is obtained via a puncture. This examination is performed with ultrasound supervision in order to reduce the danger of hitting the fetus or placenta and thereby harming the gestation.
The following can be determined from a chorion biopsy or an amniocentesis (chorion cells, and cells in the amnion fluid):
- Diagnosis of chromosomal aberrations
- Prenatal sex determination
- Diagnosis of congenital metabolic disease
- Determination of neural tube defects and other abnormalities (only with amniocentesis) by measurement of the concentration of alpha-fetoprotein
- Monogenic hereditary diseases (e.g., cystic fibrosis)
- Immunogenetic determinations (HLA haplotypes)
Umbilical blood sampling
After the 20th WoP, the umbilical cord can be punctured. Umbilical blood sampling is performed when hemoglobin pathology, coagulation pathology or viral embryopathy is suspected.