The role of fetal Doppler ultrasound

This article is professionally consulted by Master, Doctor Ta Quoc Ban - Obstetrician and Gynecologist, Department of Obstetrics and Gynecology - Vinmec Phu Quoc International General Hospital.

Doppler ultrasound technique is one of the methods of fetal ultrasound that plays an important and very necessary role in obstetrics. Fetal Doppler ultrasound helps monitor and evaluate the normal and healthy growth rate of the baby while in the womb.

Doppler ultrasound, also known as color ultrasound, is the leading ultrasound technique widely used today. Doppler ultrasound technology uses continuous waves to detect the direction and velocity of flow in the body. Therefore, fetal Doppler ultrasound in obstetrics has the effect of measuring the flow of blood vessels, examining the fetal heart and some functions that other fetal ultrasound techniques cannot perform. Specifically, Doppler ultrasound also helps measure the impedance index of the umbilical artery, middle cerebral artery in the fetus.
Because Doppler ultrasound uses high-frequency waves that are not found in nature, the diagnostic value is very high. From each received frequency signal, the machine will synthesize and display it on the screen in the form of different colors or spectral waves, sometimes even an audible signal.
Similar to all other types of ultrasound, fetal Doppler ultrasound is considered safe, painless and does not endanger the health of the fetus if performed as prescribed by a doctor for 3 months. late pregnancy. However, there are still some cases where the doctor will order a Doppler ultrasound earlier and more often. If fetal Doppler ultrasound is required at an early stage, it should be performed with the lowest energy level (thermal index TI 1.0) and the shortest exposure time (no longer than 5-10 minutes and not lasting > 60 minutes).

Doppler ultrasound is usually divided into 2 main types: continuous Doppler and pulse Doppler. However, continuous Doppler technique is not commonly used in obstetrics, except in some cases of fetus with coarctation of the aorta or tricuspid regurgitation. At this time, Continuous wave doppler (CW Doppler) can be useful in determining the maximum velocity of very high velocity flow, limiting over-threshold.
Meanwhile, pulsed Doppler fetal ultrasound can distinguish signals at different depths. The doctor will use a crystal as both transmitter and receiver, in which sound waves are transmitted in series of pulses and along the scanning direction of the transducer. The size and depth of the sampling area can also be adjusted on the machine.
In addition, to evaluate the maternal-fetal circulation, there are other modes such as spectral Doppler, energy Doppler (Power wave Doppler - PW Doppler) and flow color spectrum, or dual Doppler (Duplex Doppler).

In general, asking the mother to perform fetal Doppler ultrasound in obstetrics will help:
Measure blood flow in each part of the fetal body (umbilical cord, brain and fetal heart) to determine the ability to absorb get enough oxygen and nutrients the baby needs; Observe and evaluate the status of blood flow through the arteries - veins to diagnose the normal condition, as well as the healthy development of the fetus; Screening for some pathologies (eg congenital heart) and birth defects of the fetus in order to provide the earliest remedial measures; Monitor and detect abnormal signs in the fetus, if any, to prevent low birth weight babies; Assess the appropriate time to take the baby out. Depending on the mother's condition and suspicions about pregnancy, the doctor will specify the specific area and part that needs Doppler ultrasound. However, in cases where both mother and child are healthy, this ultrasound technique should not be abused.

3.1. Uterine artery Doppler ultrasound The uterine artery plays a very important role, responsible for conducting blood to the mother's uterus to provide oxygen and nutrients to the healthy developing fetus in the womb. Therefore, Doppler ultrasound of the uterine artery will help the doctor check that the placenta is having an adequate blood supply. Because if the placenta does not receive the necessary amount of blood, the fetus cannot receive enough oxygen and nutrients through the umbilical cord.
Doppler ultrasound of the uterine artery can be performed with transabdominal or vaginal transvaginal transducers, and is only applicable in women with normal uterine anatomy (no congenital anomalies in the uterus). uterus)
3.2. Umbilical artery Doppler ultrasound The umbilical cord is the bridge to supply oxygen and nutrients to the fetus. To check the flow of blood from the placenta to the umbilicus, doctors may use the umbilical artery Doppler ultrasound technique. Commonly indicated cases of umbilical artery Doppler ultrasound include:
Fetal growth retardation (small gestational age difference); The fetus is affected by incompatible Rh antibodies; Women who are pregnant with multiples (identical twins), have a BMI that is too high / low, or have diseases such as high blood pressure, diabetes.. Have a history of low birth weight babies, late miscarriages or babies death shortly after birth. Early-onset fetal growth retardation (before 34 weeks) will show signs of placental dysfunction such as increased umbilical artery resistance and decreased middle cerebral artery flow resistance. Conversely, late-onset fetal growth retardation (after 34 weeks) will present with signs of acidosis or increased risk of fetal death, as demonstrated by loss/reversal of umbilical artery diastolic waves and Doppler abnormalities. venous tube.
In summary, umbilical artery Doppler is a standard parameter to identify early-onset delayed fetal growth (before 34 weeks), but not a valuable parameter for detecting late-onset cases after 34 weeks. Most late-onset slow-growth fetuses with poor outcomes have normal umbilical artery Doppler.

3.3. Middle cerebral artery and ductus venosus In the case of abnormal findings after performing Doppler ultrasound of the umbilical artery (increased impedance, wave loss or diastolic wave reversal), the doctor may prescribe Continue to investigate blood flow by pulsed Doppler ultrasound of the veins or the middle cerebral artery. In particular, the ductus venosus is a source of nutritious oxygen-rich blood to the brain and heart of the fetus. When the fetus is severely hypoxic or acidosis occurs, redistribution of oxygen-rich blood from the umbilical vein to the ductus venosus occurs.
Fetal doppler ultrasound helps to examine, diagnose and evaluate the health of the fetus. In particular, the function of checking necessary nutrients and oxygen is something that conventional fetal ultrasound cannot do. In general, pregnant women who are in the last 3 months of pregnancy can conduct fetal Doppler ultrasound during regular antenatal check-ups at the request of the doctor, to ensure that the baby is developing in the best way.
Vinmec International General Hospital has full professional qualifications and technical means to effectively perform prenatal examination methods, including fetal Doppler ultrasound. There is a team of well-trained and experienced obstetricians, a complete and modern medical equipment system, professional service quality, effective diagnosis and treatment. contribute to the protection of pregnancy health for both mother and baby.
Master. Doctor Ta Quoc Ban is formerly a Lecturer in the Department of Obstetrics and Gynecology, University of Medicine and Pharmacy - Thai Nguyen University, Doctor of Obstetrics and Gynecology at Thai Nguyen Central General Hospital, Deputy Head of the Department of Obstetrics and Gynecology at the Hospital of Medical University. The doctor has full practice certificates in the field of obstetrics and gynecology such as ultrasound, laparoscopic surgery, endoscopic and electrocautery, artificial insemination (IUI)...