Prenatal diagnostics are quick and indicate whether your baby is healthy – but they are not 100% accurate. They merely calculate the risk of health problems and many couples prefer to do without. No one is obliged to undergo these tests; you have the right not to know. The vast majority of babies are born healthy; only 2% to 4% are born with a birth defect.
Definition of prenatal diagnostics: Not all prenatal examinations are defined as prenatal diagnostics in the strictest sense of the term. For instance, testing for antibodies in the mother’s blood or regular urine tests do not come under this umbrella term. Prenatal diagnostics refer instead to the identification of specific hereditary diseases such as chromosomal abnormalities (Down’s syndrome is the most common) or rare single gene disorders known to be present in the family.
Reliability and risk of tests: There are not (yet) any prenatal tests that can detect the wide range of congenital disorders, chromosomal abnormalities and genetic defects with 100% accuracy and no associated risk (e.g. miscarriage). Furthermore, in the majority of cases, prenatal diagnostics can’t make a prognosis on the severity and individual characteristics of any potential disability. Very often, the pregnant woman is under pressure to decide quickly whether to terminate the pregnancy or not.
Invasive tests in the first trimester: These tests involve extracting cells from the foetus in the uterus to reliably asses the chromosomes or genes of the unborn child. Invasive tests are always associated with a small risk. Examples:
Non-invasive tests in the first trimester: These tests enable doctors to make an assessment using indirect means. Examples:
First trimester test between 11th and 14th week of pregnancy: blood test to determine hormone and protein values. An ultrasound scan is carried out at the same time. By measuring the foetus’ nuchal translucency and factoring in the mother’s age, blood test results and week of pregnancy, a computer program can help calculate a statistical risk factor to identify a foetus with trisomy 21, another chromosomal deviation or a neural tube defect (e.g. open spine). The first trimester test calculates a statistic risk value only; it is not a diagnosis. The results are available within a week.
If abnormal values are identified, a non-invasive prenatal test is performed in most cases. If the test indicates a very high risk, invasive tests such as chorionic villus sampling or amniocentesis are recommended instead.
Non-invasive prenatal testing (NIPT)
NIPT involves taking a blood sample from the mother to analyse the foetus’ DNA. The test can be performed from the 12th week of pregnancy and poses no risk to the foetus. NIPT can confirm with a high level of accuracy whether the foetus suffers from a genetic disorder, such as trisomy 21 (Down’s syndrome), trisomy 18 (Edward’s syndrome) or trisomy 13 (Patau syndrome). As with the first trimester test, NIPT is a screening, which means it’s not diagnostic. If the result is positive or unclear, it should be confirmed or clarified with an invasive test, because NIPT can deliver a false positive result.
Regular ultrasound scans from the 5th week (arrange consultations with your doctor) serve the following purposes:
Nuchal translucency screening between the 11th and 13th week to determine whether the foetus has Down’s syndrome
Analysis of mother’s blood (serum screening) from 8th to 20th week