Genetic diagnostic tests during pregnancy
Detecting risks early
Prenatal genetic diagnosis is a test performed during pregnancy to detect certain chromosomal or genetic abnormalities in the baby.
When is prenatal diagnosis offered?
It is offered when there is an increased risk of a genetic condition, such as: • a family history of a genetic disorder • a high risk of a chromosomal abnormality found during screening tests • the discovery of fetal anomaly(ies) during an ultrasound • a chromosomal abnormality in one of the parents
How is the test performed?
There are two methods used to collect cellular material from the baby:
Chorionic villus sampling
This involves collecting a small sample of placental tissue (chorionic villi) at the end of the first trimester. The test is typically performed from the 11th week of gestation.The sample is taken either through the cervix or the abdomen under ultrasound guidance.
Amniocentesis
This involves collecting a small amount of the fluid surrounding the fetus in the uterus (amniotic fluid) using a needle inserted through the mother’s abdomen. The test is generally performed from 15 weeks of gestation and can be done until the end of the pregnancy.
Both procedures are conducted in an outpatient setting and do not require anesthesia. They carry a risk of pregnancy loss estimated between 0.5% and 1%.
What tests can be performed on these samples?
QF-PCR rapid testing
Rapid and targeted detection of trisomies 13, 18, 21, and sex chromosome aneuploidies (results within 24–48 hours). This test is performed on DNA extracted from amniotic fluid or chorionic villi using a quantitative fluorescent PCR kit.
Karyotype analysis
This test is often requested to confirm a high risk of trisomy 21 detected during screening. It identifies the specific type of trisomy 21 the baby carries (nondisjunction or translocation).
Array CGH (or DNA microarray)
With a resolution 100 times greater than karyotyping, array CGH detects small losses or gains of chromosomal material (deletions, duplications, or complex rearrangements).
Exome sequencing
This test looks for single-point mutations in the coding sequences of all known human genes related to fetal anomalies identified by ultrasound.
These tests do not screen for all possible fetal abnormalities or malformations.
Is it mandatory?
No, all tests are proposed, but the choice is always yours.The goal is to inform you, support you, and respect your decisions.
Published by Sonic Suisse SSD, Version 2025 Pictures provided by Dr. med. (bg) Alina Staikov, gynpoint, www.gynpoint.ch