The term prenatal diagnosis describes various practices (invasive and non-invasive) of prenatal diagnosis. These practices serve the purpose of detecting high-risk pregnancies, high-risk childbirths as well as disturbances of health at an early stage and hence to avert in time danger to life and health of both mother and child.

In contrast to the non-invasive methods of PND, the invasive methods of PND deliver reliable results. In a suspected case, the physician can advise the pregnant woman to make use of invasive methods of PND subsequent to the application of non-invasive methods. The invasive methods first and foremost include the following three methods:

1. The chorionbiopsy is the earliest possible form of invasive PND. During such a biopsy, the physician extracts some tissue out of the chorion (the infantile part of the placenta which is not yet fully developed) in order to be able to detect possible genetic particularities or certain metabolic diseases of the child. A chorionbiopsy can be conducted at the earliest in the ninth week of pregnancy, usually it is performed from the eleventh week onwards. Tissue is removed either by means of a needle, which is inserted through the mother's abdominal wall, or by means of the insertion of a thin plastic hose over the cervix. In order to avoid hurting the child, both methods determine the position of the child as well as that of needle and hose by means of ultra sound. If this examination results in a diagnosis of diseases of the child, these are mostly diseases for which no therapy in the sense of a causal cure exists. Therefore, the consequence of such a finding is either that the parents accept the child with its diagnosed characteristics or that they give the child free for adoption after it is born or that they decide in favour of an abortion.
2. During an amniocentesis (examination of the amniotic fluid), which is oftentimes conducted between the 15th and 16th week of pregnancy, amniotic fluid is extracted by means of inducing a needle through the abdominal wall into the amnion. This serves the purpose of examining cells contained in the amniotic fluid that have been pushed off by the fetus. For the chromosome analysis, these cells are multiplied in the laboratory. Apart from data which cannot be treated, such as chromosomal anomalies, this examination methods provides further findings which can be treated, including blood group incompatibilities of mother and child or lung maturity in the case of an impending premature delivery.
3. A cordocentesis (umbilical cord puncture) is possible from approximately the 14th week of pregnancy onwards. During such a cordocentesis, blood is extracted from the umbilical cord by means of puncture and is then being examined as to its composition. It is, for instance, possible to preclude or diagnose anemia, infections, blood group incompatibilities etc. judging from the presence of consicuous blood levels.

In comparison to the non-invasive methods of PND, the invasive methods are more reliable but are also much more risky. While the non-invasive methods are ranked as mostly safe, the National Ethics Council in its statement "Genetic diagnosis before and during pregnanc" (unofficial translation) ("Genetische Diagnostik vor und während der Schwangerschaft") of 2003 explicitly points towards the risks of infections, bleedings and pains resembling contractions in pregnant women as well as to the risk of injury for the unborn child, which are connected to the implementation of invasive methods of PND.

The invasive methods of PND are the most risky prenatal examination methods. The risks of miscarriage after invasive methods lies at two to four per cent concerning chorionbiopsy with access through the cervix; concerning chorionbiopsy with access through the abdominal wall, the risks lie at one to two per cent. As regards the fetal blood puncture, the risk is at more than one per cent and for the amniocentesis the risk of having a miscarriage lies at less than one per cent.