What does Doppler ultrasound show?
Doppler testing evaluates not structure, but function - how effectively the fetus is supplied with blood. Three key areas are measured. The uterine arteries reflect the quality of placentation: increased resistance in them is associated with the risk of preeclampsia and growth retardation. The umbilical cord artery shows the resistance of the vascular bed of the placenta - an increase in indices, and especially zero or reverse diastolic blood flow, is a serious alarming sign. The fetal middle cerebral artery reveals the so-called centralized circulation, when the fetal body redistributes blood in favor of the brain during hypoxia.
The cerebro-placental ratio is calculated separately - the ratio of the indicators of the cerebral artery and the umbilical cord artery. It often changes before each of the indicators individually goes beyond normal limits, and is therefore considered a sensitive early marker of fetal distress.
The main indications are fetal growth restriction, preeclampsia and arterial hypertension in the mother, diabetes mellitus, multiple births, complicated obstetric history, decreased movements, oligohydramnios. The volumetric 3D/4D mode in this version of the study is performed additionally after the functional part of the protocol is completed.
Why are planned studies needed?
Ultrasound is the main tool for monitoring pregnancy. It confirms that the fetus is alive and developing on time, shows the number of fetuses, the position of the placenta, the volume of amniotic fluid and the condition of the cervix. Most serious malformations are detected by ultrasound, and at a time when it is still possible to make an informed decision.
There are usually three planned examinations during pregnancy - one in each trimester, in strictly defined windows. Outside of these periods, some measurements lose diagnostic value: for example, the thickness of the collar space can be correctly assessed only from the 11th to the 13th week plus 6 days.
Safety of ultrasound during pregnancy
Ultrasound is not ionizing radiation: it does not accumulate in tissues and does not have a radiation dose, unlike X-rays and computed tomography. Over decades of use, no data have been obtained on the harmful effects of diagnostic ultrasound on fetal development.
In this case, the principle of reasonable sufficiency applies: the study is performed according to indications and in the optimal time frame, and the power and exposure time are kept at the minimum required level. This applies separately to the Doppler and 3D/4D modes - they are used consciously, and not “just in case” at each visit.
What affects image quality
The clarity of the picture depends on the age, position of the fetus, the thickness of the anterior abdominal wall, the amount of amniotic fluid and the presence of a scar on the uterus. If the fetus turns its back to the sensor or covers its face with its hands, some structures cannot be examined.
In such cases, the doctor may ask you to walk, change your body position, or come back in a few days. This is not a sign of pathology, but a common technical situation, especially common during 3D/4D examination.