In every pregnancy, at least three ultrasound examinations should be performed in the sense of screening, according to the maternity guidelines. They should be performed at approximately the 10th, 20th, and 30th weeks of pregnancy, respectively. During the first ultrasound examination at about the 10th week of pregnancy, vitality criteria of the embryo are searched for. These are mainly heart actions or movements. In addition, the position of the placenta (placenta) is described and the date of birth is calculated. During the second ultrasound examination in pregnancy, which is performed between the 18th and 22nd week of pregnancy, the quality criteria of the DEGUM (German Society for Ultrasound in Medicine; DEGUM I) in fetal sonography (synonyms: fetal ultrasound diagnostics; fine diagnostics; malformation diagnostics) are to look primarily for indications of malformations. If such indications are detected, the pregnant woman should be referred to a center with DEGUM level II prenatal diagnostics.The noninvasive molecular biological blood test (NIPT) for prenatal diagnostics for trisomies does not eliminate the need for prenatal diagnostics by ultrasound:Note: 90 percent of fetal or infant malformations are not chromosomal in origin at all. The patient should be informed that unfavorable ultrasound conditions can lead to limitations in the validity of the examination method. These conditions include, above all, obesity (obesity), an unfavorable position of the fetus, oligohydramnios (amniotic fluid volume < 500 ml) or other limitations such as a scarred abdominal wall of the pregnant woman. Furthermore, it is important to remember that not all malformations can be detected sonographically.
Indications (areas of application)
Increased attention should be paid to the following indications during ultrasonography (they are considered indications for further ultrasonography according to DEGUM level II):
- Deviations from the normal head shape, such as short-headedness or broad-headedness with flattening of the back of the head
- Changes/absence of intracranial structures.
- Changes in neck shape such as hygroma colli – tissue proliferation in the area above the clavicle.
- Deviations from normal thoracic shape with changes to normal heart position and configuration, including cardiac arrhythmias
- Changes or absence of sections of the gastrointestinal tract or genitourinary system.
- Fluid accumulation in the abdomen (abdominal cavity).
- Contour irregularities of the back such as spina bifida (open back).
Other indications for further DEGUM level II ultrasound examination besides abnormalities on ultrasound examination are:
- Anamnestic risk
- Risk on the part of the mother or child
- Psychological stress on the mother
- Examination before planned further diagnostics (as described below).
If indications of a malformation have occurred during the examination, the following further examinations (so-called fine diagnostics) should be performed. This includes depending on the indication from the sonography:
- Amniocentesis (amniocentesis).
- Chorionic villus sampling – tissue sampling from specific areas of the placenta (placenta).
- Cordocentesis – puncture of the umbilical cord.
- Intrauterine transfusion – blood exchange in the womb.
- Fetal puncture
- Shunt insertion – insertion of a short circuit connection, such as may be performed on the unborn child in cases of fetal urologic disease such as megacystis (severe dilatation of the urinary bladder)
- Amniotic infusion – amniotic fluid replenishment in cases of severe oligohydramnios (amniotic fluid volume less than 500 ml).
- Fetoscopy – imaging of the fetus in the womb.
During ultrasound examinations at 20 and 30 weeks of pregnancy, the course and development of the fetus is examined. About the biometry (fetometry / measurement of the fetus) growth retardations (growth delays) can be detected. Abnormalities in Doppler sonography (ultrasound examination that measures the flow rate of blood in the vessels (arteries and veins)) can indicate placental insufficiency (placental weakness, i.e. the placenta cannot supply the fetus sufficiently). Other clues
- Sonographic diagnosis at 35-34 weeks of gestation reveals a quarter of fetal anomalies that were previously undetected. The most common developmental abnormalities diagnosed late were mild ventriculomegaly (abnormal enlargement of the ventricles), ventricular septal defects (malformation of the heart (heart defect) in which the cardiac septum between the ventricles (septum interventriculare) is not completely closed), double kidneys, ovarian and arachnoid cysts (ovarian cysts and malformations of the middle cobwebby meninges (arachnoid)).
- Fetal magnetic resonance imaging (MRI) is available as a confirmatory and complementary diagnostic modality for sonographically diagnosed fetal pathologies: esp. CNS anomalies and thoracic malformations can be better visualized with this procedure. The most frequent indications in the context of CNS diagnostics by means of fetal MRI are ventriculomegaly (e.g., due to hydrocephalus in aqueduct stenosis), arachnoid cysts, bar agenesis, and changes in the posterior fossa (especially Dandy-Walker malformations).
- The frequency and duration of prenatal ultrasound examinations were not associated with autism spectrum disorders in children in a case-control study.
