The ultrasound (UZ) diagnostics utilize the physical principle of propagation and reflection of acoustic waves of high frequencies.
The basis is a two-dimensional (2D) picture enabling a view of sectional planes of tissues and internal bodies of the foetus with a high accuracy and in the real time. By this method it is also possible to monitor the movement of the foetus or the activities of the foetus’ heart. On the picture you can see the face profile of the foetus in 12 th week of pregnancy.
Three dimensional (3D) or four dimensional (4D) plastic depiction is created by a computerized reconstruction of a series of 2D sectional views. At our workplace we use the 3D depiction for supplementing and documenting the findings, which have been identified, by for our clinic standard and obligatory, two dimensional examinations. For parents there will be an interesting plastic 3D picture of the foetus from the half of the pregnancy, as shown by the following picture.
Dopplerometry is used mainly when examining blood flow through the heart and vessels of the foetus: for example, through the umbilical cord, aorta, vessels supplying the kidneys, lower and upper vena cava or through the vascular shunts of the foetus (ductus venosus and ductus arteriosus). Dopplerometry informs one about the formation of the heart, function of the heart valves, function of the placental vascular bed, and thus also indirectly about the state of the internal environment of the foetus. The depiction of the blood flow through the ductus venosus (the connection between the vein of the umbilical cord and the heart of the foetus) is a significant indicator of the state of the foetus already at the beginning of pregnancy. The following picture shows the coloured Doppler depiction of the blood flow through the foetus’ kidneys:
More pictures on www.uzvidim.cz
In pregnancy four basic UZ examinations should be performed:
- First examination between 6th - 8th week, counting from the first day of the last menstruation period (PM). It is usually performed through the vagina (vaginal probe). The aim is to determine the age of pregnancy and the number of embryos (single, twins, triplets…), but mainly to demonstrate the location of the embryo in the uterus and to exclude the danger of metacyesis. From 6th week of a normal pregnancy in the uterus, a cavum can be seen, within which the so-called vitelline saccule and foetus’ disc with a visible heart activity gradually appears.
- Another examination is performed at the embryonic age of 11 weeks + 3 days up to 13 weeks + 6 days, when the stage of the pregnancy can be accurately determined by measuring the distance between the sinciput and coccyx of the foetus (CRL). An important sign is the height of effusion of hypodermis on the nucha (nuchal clearing - NT), which should be lower than 3 millimetres. A distinct enlargement of the NT means a risk of an inborn defect or a threat of miscarriage. If the foetus is turned into a favourable position, it is possible to measure the size of the nasal bone (NB). Missing or a short nasal bone means an increased risk of inborn defects. Apart from these standard signs (markers) of the inborn defects it is possible to examine the structure of the foetus’ body and determine the location of the forming placenta. In case of a multiple pregnancy it is determined whether the siblings are mono- (i.e. identical) or multizygotic.
- Examination between 20th and 22nd week of pregnancy ("genetic ultrasound"). Within this stage it is possible to accurately examine the structure of the foetus’ body and the location, shape and size of most of the internal organs. In case of the heart and kidneys we can also examine their function. The appropriate sections of the foetus are measured – usually the diameter and circumference of the head (BPD, HC), circumference of the abdomen (AC) and the length of the femur (FL). In relevant cases it is also looked for small (soft) markers of the inborn defects. These are such alterations of a normal UZ picture, which do not represent an anatomic or functional disturbance, but they do occur more frequently in cases of foetuses affected by an inborn defect than in the cases of sound ones. This especially refers to the thickness of the skin fold in the scruff of the neck (NSF), clear bright point in the left cardiac chamber (ICLV), slight extension of the renal pelvises (pyelectasia), lighter (hyperechogennous) demarcation of the intestinal walls of the foetus and a shorter femur (FL). Again, it is possible to measure the nasal bone (NB). The state and placement of the placenta is also assesed, together with the quantity of the amniotic fluid.
- Examination in 30th – 32nd week of pregnancy. This period is the basis for a biometric examination – measurement of the foetus with respect to the foetus’ size. Again, the size, shape and placement of the internal organs is evaluated together with the state and placement of the placenta and the quantity of the amniotic fluid. Additionally, it is also possible to state the so-called biophysical profile, which is an assessment of the foetus’ activity and conditions, which are in the uterus.
Safety: The ultrasound waves have a very low energy and biologic activity and therefore the UZ is a safe examination method.