The term prenatal diagnosis describes various procedures (invasive and non-invasive methods) of prenatal diagnosis. The procedures serve to detect high-risk pregnancies, high-risk childbirths and disturbances of health at an early stage and thus to avert in time dangers for life and health of mother and child.

Non-invasive methods of PND are such prenatal examinations that do not invade into the body of mother or child. This includes various forms of sonography (acoustic discharge measurement) as well as the serological examination (blood samplings of the mother). The side-effects of non-invasive methods for mother and child are assumed to be minimal. Invasive methods of PND are those procedures that intrude into the body of the woman or even the embryo by means of punctuation through the uterine wall. In contrast to non-invasive procedures, these methods deliver actual diagnoses. Noteworthy are particularly the chorionbiopsy, the amniocentesis and the cordocentesis.

The pregnancy is divided into thirds (first, second and third trimester), which means three segments of approximately three months each. Following the maternity-guidelines of the federal joint committee of physicians and health insurances, an ultrasonic examination is conducted in each trimester within the scope of a routine pregnancy screening-examination. The compulsory health insurance fund bears the costs for the three examinations. They serve the purpose of checking certain fetal features. A fetometry, for instance, measures the head circumference and diameter, the abdominal girth and the length of the thigh bone; out of this, inferences can be made as to certain characteristics of the child such as height and weight.

The first ultrasonic examination can, amongst others, determine whether a singleton pregnancy, a multiple pregnancy or a tubal pregnancy is present. Furthermore, first fetal cardiac activities can be demonstrated. By means of this early ultrasonic examination, malformations can be determined at an early stage (for instance, the diagnosis of an empty amniotic cavity without any amniotic fluid, allows the conclusion that the embryo will not be able to develop further in a regular way). The determination of lengths and diameters on the embryo give information about its timely development. Malformations on the head can be determined partially.

There is no therapy setting in at an early stage regarding the treatment of malformations of the child that were detected during the first ultrasonic examination; the medical scope of action is hence largely restricted.

During the second ultrasonic examination, the embryo's physical build and inner organs can be better identified. Measurements of the motion sequences can qualitatively and quantitatively detect developmental disorders. Measurements of the extremities and the diameters of the torso, the head and the thorax provide information about a timely development. Certain parts of the body can be observed more closely by means of ultrasound insofar as there is any suspicion as to the possible presence of a cleft lip and palate or spina bifida (split spine).

The last ultrasound screening examination serves the purpose of preparing for the child birth. The position of the child and of the placenta can be determined and this information can then be included in the birth prognoses. Within this phase of pregnancy, most cardiac defects are detected, whereby first sporadic therapeutic actions for the child can be taken.

Apart from the three ultrasonic examinations, the maternity-guidelines also arrange for certain routine serological examinations. These include the rubella haemagglutination inhibition-test (HAI), possibly an HIV-test, the determination of the blood group and of the rh-factor D and an antibody screening procedure.

Going beyond the routine preventive medical check-up, one or more PND-methods that are not used routinely can be applied in certain cases. This concerns individual health services that are generally not born by the compulsory health insurances unless an indication is present. Such methods are applied only in suspected cases and only following the explicit wish of the parents because they are connected to certain risks. Due to the risks and the fact that a diagnosis can cause severe emotional stress for the parents, there is an obligation on the part of the physician to provide counselling before, during and after the examination.

In detail, the non-invasive PND-methods that are not conducted routinely include the measurement of the nasal bone, the triple-test/quadruple-test, a measurement of the nuchal translucency, doppler-sonography and 3D-ultrasound/4D-ultrasound-examinations.

If the fetometry renders results that deviate from the mean, it is possible to obtain a more precise image by means of further sonographies such as precision ultrasound ("organscreening"), doppler-sonography and 3D-ultrasound/4D-ultrasound-examinations. By means of precision ultrasound, "sonographic softmarkers" can be detected; these are features, which, statistically, occur more frequently in unborn children who have a chromosome anomaly (for instance trisomy 21: "Down-Syndrome") or a malformation.

The doppler-sono aims particularly at detecting disorders in organ functions such as cardiac insufficiencies. Both methods also provide an indication for the possible presence of further malformations (e.g. cleft palate). By means of 3D- and 4D-ultrasound, potential findings of prior sonographies can be checked again and can be judged more precisely as to their peculiarity and their ability to be treated.