Examinations
Examinations
Fetal chromosomal abnormalities screening is conducted to determine the possibility of chromosomal disorders, including Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome), and Trisomy 13 (Patau syndrome).
Down syndrome is a chromosomal disorder caused by an error in meiotic cell division during sperm or egg maturation, resulting in an extra 21st chromosome. Edwards syndrome (Trisomy 18) and Patau syndrome (Trisomy 13) are less associated with maternal age but are also linked to meiotic errors.
Prenatal screening in the first trimester is performed to assess the risk of these chromosomal abnormalities between 10 weeks and 13 weeks + 6 days of pregnancy. The screening is calculated using the PRISCA (Prenatal Risk Calculation) software, which holds an international certification of compliance. The test determines the levels of free beta-subunit of human chorionic gonadotropin (β-hCG) and Pregnancy-Associated Plasma Protein-A (PAPP-A) in maternal blood.
Clinical factors must be taken into account for screening, including maternal age, weight, number of fetuses, presence and specifics of IVF conception, maternal ethnicity, smoking, diabetes, and medications used during pregnancy. Ultrasound results are also considered.
Screening results cannot serve as a diagnostic criterion or a reason for pregnancy termination. Instead, they help determine whether invasive diagnostic procedures such as chorionic villus sampling or amniocentesis are necessary for genetic analysis.
- Avoid consuming fatty foods 24 hours before the test.
- Avoid physical and emotional stress for 30 minutes before the test.
- Refrain from smoking for at least 30 minutes before the test.
- Bring an ultrasound report performed within the last 24 hours.
Prenatal screening is recommended in the first trimester (10 weeks – 13 weeks + 6 days), especially in cases where there are risk factors for fetal abnormalities:
- Maternal age over 35 years
- History of miscarriages or pregnancy complications
- Previous pregnancies affected by chromosomal abnormalities, Down syndrome, or congenital defects
- Family history of genetic disorders
- Exposure to infections, radiation, or teratogenic drugs in early pregnancy or shortly before conception
Risk Calculation and Interpretation
Based on the test results, the PRISCA software calculates the probability of a fetal chromosomal disorder.
For example, a 1:400 ratio means that statistically, one out of every 400 women with similar test results will give birth to a child with a chromosomal abnormality. A result of 1:250 or lower is considered high risk, warranting additional diagnostic procedures.
Next Steps for High-Risk Cases
If the screening test indicates a high risk, further diagnostic procedures are required:
- Non-Invasive Prenatal Testing (NIPT, from 10 weeks) – analyzes fetal DNA in maternal blood. It has higher accuracy (~99%) than biochemical screening for Trisomy 21, 18, and 13.
- Chorionic Villus Sampling (CVS, 10–13 weeks) – involves sampling placental tissue for genetic testing.
- Amniocentesis (15–20 weeks) – involves analyzing fetal cells from amniotic fluid to confirm chromosomal abnormalities.