Prenatal diagnostics: is my baby healthy?
Prenatal examinations are used to identify serious illnesses, malformations and disorders in the foetus at an early stage. But prenatal diagnostics also involves risks, so it’s important to be well informed about the different procedures.
It goes without saying that all expectant parents hope that their child is born healthy, so prenatal examinations are a standard part of every pregnancy. If the results of the first detailed check-up – in Switzerland this usually takes place some time in the second or third month – are normal, the mum-to-be has seven further routine check-ups in the run-up to the birth. However, if a high-risk pregnancy is determined, for example due to the woman’s age or family history, prenatal diagnostics can provide more information on the embryo’s health. These tests can be used, for example, to estimate the risk of malformations and hereditary illnesses (e.g. trisomy 21).
Non-invasive prenatal tests
Prenatal diagnostics differentiates between invasive and non-invasive tests. The term “non-invasive” means that the tests don’t penetrate the uterus. It therefore poses no risk of miscarriage or of injury to the unborn child.
- Measuring nuchal translucency: The thickness of the liquid poster on the neck of the unborn child may be an indication of a chromosomal defect. Taking this measurement by ultrasound is a standard test carried out in the 11th to 13th week of pregnancy. The interpretation of the ultrasound is dependent on the doctor’s experience.
- First-trimester test: If the result of the nuchal translucency measurement identifies abnormalities, a first-trimester test is usually carried out. In this case, the mother’s blood test results, her age and the foetus’ nuchal translucency are used to calculate a statistical risk factor for a chromosomal abnormality. The first trimester test provides only a statistical value calculated by a computer program; it is not a diagnosis.
- Non-invasive prenatal testing (NIPT): If the first-trimester test shows a risk of 1:1000 or higher for trisomy 21, 18 or 13, the expectant parents can choose to have the child’s DNA tested in the mother’s blood. An analysis of the mother’s blood is possible from the 12th week of pregnancy. NIPT can detect a genetic abnormality such as trisomy 21, 18 or 13 with a high degree of accuracy. But it is not 100% reliable. Like the first-trimester test, NIPT provides a statistical value, not a diagnosis. Therefore, in the event of a positive or unclear result, many doctors recommend an invasive test for clarification.
- Detailed ultrasound: Between the 19th and 22nd week, it is possible to examine the foetus’ organs using a level 2 ultrasound. If parents know before the birth that their child requires special treatment, they can consult specialists early on.
Invasive prenatal tests
With invasive tests, the specialist takes a sample of the amniotic fluid, blood from the umbilical cord or tissue from the placenta to examine cells of the foetus directly. Invasive tests deliver relatively precise results, but they are associated with specific risks.
- Chorionic villus sampling (CVS): A fine needle is used to remove a sample of chorionic villi from the placenta through the abdominal wall for testing in the laboratory. The results are available in a few days. This invasive test is usually carried out between the 10th and 14th week after a positive or unclear NIPT result. The risk of a miscarriage is 0.5 to 1.5%. If the result of the CVS is inconclusive, there is the option of amniocentesis.
- Placental biopsy: From the 19th week of pregnancy onwards, the test is known as a placental biopsy instead of chorionic villus sampling.
- Amniocentesis: During amniocentesis, fluid is taken from the amniotic sac with a thin needle. It takes two to three weeks to analyse the amniotic fluid sample, because the cells have to be cultivated in the laboratory. As this examination is usually performed between the 14th and 18th week of pregnancy, the definitive result may not be available until the 21st week of pregnancy. The termination of a pregnancy at this time means that the birth has to be induced. The risk of a miscarriage following amniocentesis is low at less than 1%.
- Cordocentesis: Blood drawn from the umbilical cord is rare and only possible from the 18th week of pregnancy. The risk of a miscarriage is 1 to 2%. This procedure is mainly used in cases of suspected blood group incompatibility or foetal anaemia.
Parents can choose whether and which prenatal tests they want to have done. Before any examinations are carried out, they should be clear about what the tests involve and whether an abortion is an option for them at all. In addition, certain risk factors have to be met for the costs of prenatal diagnostics to be covered by the health insurer.