The most important facts about prenatal diagnostics
What is prenatal diagnosis?
Prenatal diagnostics (PND) is a branch of medicine that has developed progressively in recent years and is still undergoing great change. In general, one can imagine a prenatal examination on the fetus and the pregnant woman, which is primarily non-invasive, but from the outside by means of ultrasound.
Ultrasound-based exams include:
- Combined test and preeclampsia screening in the first trimester
- Growth controls of the child
- Fine diagnostic ultrasound
- Doppler examinations
- 3D & 4D ultrasound
These examinations are subject to well-defined quality requirements and should therefore serve as a supplement to the intended maternity tests. Since malformations also have to be thought of as a genetic cause, the further clarification consists in carrying out genetic diagnostic tests to detect changes in a gene.
What can prenatal diagnostics determine and what it can't?
This specialty is very complex and consists essentially of an ultrasound-based diagnosis and in special situations of a genetic diagnosis together. For families in which there are established genetic syndromes a comprehensive prenatal consultation and clarification has to be carried out. In principle, work is done according to national and international standards or guidelines. Nevertheless, as everywhere in medicine, there are limits here as well - congenital changes could appear late in pregnancy or sometimes only after birth.
Which are the available invasive and non-invasive methods?
The term non-invasive methods include first-trimester screening (Combined Test: week of pregnancy (SSW) 11 + 0 - 13 + 6), usually in conjunction with a pre-eclampsia screening (risk calculation for a pregnancy poisoning), the organ screening from the 20 to about 23 weeks gestation and the non-invasive prenatal test (NIPT - from the 10th week of pregnancy).
Pediatric and maternal blood flow measurements in various vessels using Doppler sonography make it possible to measure the state of care. Likewise, one can hereby receive an indication of a child's anemia .
By using 3D ultrasound, fetal structures can be better assessed. The Combined Test focuses on the 3 most common chromosome disorders:
- Pätau syndrome
In addition, 50% of malformations can be detected at this time .
Based on the maternal age, the gestational age, a skin fold measurement, the representation of the nasal bone and in combination with pregnancy hormones there is a chance for the three above-mentioned chromosomal changes cto be alculated . The accuracy is around 90-95%.
Another test procedure for Down syndrome, Edwards syndrome, and Pätau syndrome, either as a primary screening for trisomy 21 or in combination with the combined test, is NIPT (non-invasive prenatal testing). The analysis is done by taking a blood sample .
The NGS ( Next Generation Sequencing ) based method is now offered by several companies with validated testing methods and helps to quantify excess of pediatric cell-free DNA, as is the case with Down's syndrome, for example, from maternal blood. Furthermore, the determination of sex chromosomes with this method is possible.
The use of these tests is possible for singleton pregnancies and also for twin pregnancies .
It should be mentioned that the implementation of an NIPT without ultrasound is not recommended.
In addition, one can at the same time in the first trimester calculate a risk for pregnancy complications (preeclampsia), especially for pregnant women with risk factors such as:
- Diabetes mellitus,
- Existing hypertension,
- Autoimmune diseases,
- After IVF treatment (artificial insemination),
- If pre-eclampsia has occurred in pre-pregnancy
The organ screening in the second trimester (gestational age) is carried out according to guidelines, created by various ultrasound companies and serves to represent structural changes in the unborn child.
For abnormalities in ultrasound (US), therefore, an invasive clarification is offered. Depending on the gestational age, a CVS (puncture of the suckler cake) or an AC (amniotic fluid puncture) can be performed. After the diagnostic puncture, the recovered material is genetically analyzed to confirm a suspected diagnosis.
Another reason to diagnose invasive and also to treat is the suspicion of a child's anemia, caused for example by a Rhesus intolerance (blood group intolerance to the Rhesusfaktor antigen between mother and child). The subsequent umbilical cord puncture allows on the one hand to determine the severity of the anemia and, on the other hand, to administer to the child an adequate amount of blood via thisaccess.