Doppler sonography measures the blood flow pattern in the uterine arteries as well as fetal blood flows in arteries and veins in pregnant women. Doppler sonography can detect impending placental insufficiency (lack of placental function) as early as 19 to 22 weeks’ gestation (SSW). Doppler sonography (synonyms: Doppler effect sonography, Doppler echography) is a medical imaging technique that can dynamically visualize fluid flows (especially blood flow). It is used to assess blood flow velocity and, in cardiology, to diagnose cardiac and valvular defects. Particularly in the case of pathological vascular phenomena, Doppler sonographic examination represents the basis of the diagnostic procedure, since both the velocity distribution in the respective vessel section is assessed and an exact representation of the direction of flow can be made. Furthermore, Doppler sonography makes it possible to reflect the temporal change in the velocity of the blood flow. The factors obtained in this way can then be used to calculate the volume flow rate and the pathophysiologically important flow resistances. In addition to the diagnostic importance of the procedure in angiology, Doppler sonographic examination also plays a crucial role in obstetrics and gynecology.
Indications (areas of application)
- First-time mothers
- Multiple pregnancies
- Infantile deficiency development or gestational gestosis in a previous pregnancy.
- Maternal diseases such as hypertension (high blood pressure), diabetes mellitus, kidney disease and autoimmune diseases.
- Disorders of amniotic fluid volume – oligohydramnios (amniotic fluid volume < 500 ml) or polyhydramnios (amniotic fluid volume > 2 l).
- Suspicion of placental insufficiency (lack of function of the placenta) or assessment of the placenta (structure, size, etc.).
- Fetal growth retardation (fetal growth retardation; fetal growth restriction).
- Abnormal fetal heart sound patterns (CTG).
- Already occurred gestosis
The procedure
Doppler sonography is based on the principle that ultrasound waves are emitted at a defined frequency into the tissue, where they scatter on circulating erythrocytes (red blood cells). Due to this scattering, a portion of the ultrasound waves returns to the transducer, which thus serves on the one hand as a transmitter and on the other hand also as a receiver of the sound waves. The erythrocytes thus act as a boundary surface at which the sound waves are reflected, so that a frequency increase occurs when the distance between the transducer and the boundary surface decreases and the frequency decreases when the distance increases. However, the so-called Doppler effects occur not only in flowing blood, but also in other moving organic structures, such as vessel walls. Doppler sonography is divided into several techniques:
- Single-channel Doppler techniques: In this method, a single beam of sound is emitted by the Doppler system, so that the resulting data arise solely from the section of vascular structure through which the beam passes.
- Continuous-wave (CW) Doppler sonography: a subset of single-channel Doppler techniques, this system represents the simplest method of collecting continuous blood flow data over the entire depth of ultrasound penetration. Each transducer has separate acoustic elements for sound transmission and reception. Continuous information acquisition is made possible by the fact that the transmitter and receiver in the transducer operate in parallel and continuously side by side. However, spatial assignment is not possible with this method. However, the advantage of this method is that the determination of high flow velocities is possible.
- Pulsed-wave (PW) Doppler sonography: as a further subgroup of the single-channel Doppler methods, a spatially selective velocity measurement is possible with this system in contrast to CW Doppler sonography. In pulsed Doppler mode, an electronic measurement window is generated to measure the flow velocity of erythrocytes flowing through the measurement window at a defined depth in the tissue. Unlike the CW Doppler method, the information is transmitted via pulses and not continuously.
- Multichannel Doppler techniques (synonyms: Color Doppler sonography, color-coded Doppler sonography, color-coded duplex sonography; combination of B-scan with PW Doppler/Pulse Wave Doppler): In this technique, as in CW Doppler sonography, the sound transmitter and the sound receiver are located as separate structures in the transducer. However, the difference is that a large number of transmitters and receivers are located in each transducer. The transmission and reception of ultrasound waves do not occur simultaneously, allowing the many sound beams to gather information from a three-dimensional cross-sectional image. All multichannel systems operate in pulsed Doppler mode. The collection of information is limited by the limited number of evaluation channels in the Doppler sonograph. The large number of sound waves ensures accurate localization of information sources. Due to the functional properties of the method, it is used to estimate possible flow turbulence with the help of color coding, where different flow velocities can be represented in shades of red and blue. The turbulence itself is represented in green.
In Doppler sonography to detect placental insufficiency (placental weakness; insufficient function of the placenta), the uteroplacental (involving the uterus and placenta) stromal bed (Aa. uterinae), the umbilical vessels, the fetal aorta (fetal main artery), the cerebri mediae (middle cerebral artery), and the ductus venosus (fetal short-circuit connection between the left hepatic portal vein and the inferior vena cava) are of clinical relevance. Measured are:
- RI (resistance index; RI value; vascular resistance).
- A/B ratio (calculated from the two uterine arteries).
- PI (pulsatility index)
- AEDF (absent enddiastolic flow)
- REDF (reverse enddiastolic flow) measured.
In early fetal growth restriction (FGR) (IUGR, intrauterine growth restriction), Doppler pathologies may be present in subsequent vessels:
- Umbilical artery (UA; umbilical artery).
- Arteriae uterinae (UtA; uterine arteries).
- Ductus venosus (see above).
In late fetal WA growth restriction (“late onset FGR”) after 32 SSW), Doppler pathologies may be present in subsequent vessels:
- Uterine arteries;(UtA)
- Cerebroplacental ratio (CPR).
In the presence of impaired uteroplacental perfusion at the time of 19 to 22 weeks’ gestation, fetal growth restriction can be detected with a sensitivity (percentage of diseased patients in whom the disease is detected by use of the procedure, i.e., a positive finding occurs) of 15-70% and with a specificity (probability that actually healthy individuals who do not have the disease in question are also detected as healthy by the test)of up to 95%. Abnormal blood flow patterns (pathological flow) can provide indications of fetal insufficiency or deficiency, so that premature delivery can be performed in good time. Doppler sonographic monitoring of fetal growth restriction and obstetric management.
| Doppler sonography | Umbilical arterynot conspicuous | Umbilical arteryPI > 95th percentile | Umbilical arteryAEDF | Umbilical arteryREDF |
| Controls | every 2 weeks | at least weekly | every few days | every few days |
| – until | 38TH-39TH SSW | 37 + 0 SSW | 34 + 0 SSW | 32 + 0 SSW |
| Delivery | Delivery in a prenatal center with neonatal intensive care unit if necessary administration of antenatal corticosteroidsif necessary administration of magnesium sulfate | |||
| Doppler sonographyA.cerebri mediaPI < 5th percentileab 37 + 0 SSW | Doppler sonographyDuctus venosusPI > 95th percentileMissing a-wave/”reverse flow” a-wave. | CTGand/orOxford CTGpathologic. | ||
SSW (week of pregnancy)
