Doppler ultrasound in pregnancy

What is Doppler Ultrasound?

The Doppler ultrasound is mainly used in late pregnancy after the 26th week to check the care of the baby in the womb and to rule out pregnancy-induced diseases in the pregnant woman. With this ultrasound technique, the blood flow and the velocity distribution in the fetal and part of the maternal vessels are shown in color and acoustically. Medical studies illustrate the value of Doppler sonography, as they show a clear connection between abnormal Doppler findings and pregnancy-induced diseases such as preeclampsiaand eclampsia. In general, Doppler ultrasound can indicate disease or fetal growth disorders two to three weeks before the onset of other symptoms. It thus supplements the blood pressure measurements and blood and urine tests routinely carried out in preventive care and is now an integral part of normal prenatal care in almost all medical practices . In the meantime, it is almost always used in so-called high-risk pregnancies, i.e. if the pregnant woman is already over 35 years old, is expecting multiple births, has already had several miscarriages or her blood group is not compatible with that of the child ( rhesus intolerance ).

When is Doppler ultrasound used?

The best time for the first Doppler examination depends on the question. In general, there is no indication before the 20th week of pregnancy. However, it is routinely used as part of differentiated organ ultrasound in the 19th to 21st week of pregnancy.

What is a “color doppler”?

If a high-resolution color Doppler device is used for Doppler ultrasound, the blood flow in the vessels of mother and child can even be displayed in two colors. This is particularly helpful, for example, to diagnose childhood heart defects and abnormalities. The flow direction of the blood is shown in different colors.

Example of a Doppler ultrasound

Indications for a Doppler ultrasound

Doppler ultrasound is already seen as part of normal preventive care in most medical practices and is used in almost every ultrasound examination. In particular, it can provide information on the following indications:

• Growth retardation (suspicion of poor growth of the child and thus possible undersupply)
• Decreased amniotic fluid (can also lead to poor child care)
• Suspicion of a childhood disease, malformation or chromosomal abnormality
• Abnormal heart rate of the baby
• Suspected heart defect or heart disease in the child
• Preterm labor (shown on CTG )
• Infection (e.g. parvovirus, ringworm)
• blood group incompatibility
• Disease of the mother (high blood pressure, preeclampsia, gestosis , diabetes mellitus)
  
• multiple pregnancy
• Preterm birth or miscarriage in previous pregnancies
• Pregnancy-induced diseases in previous pregnancies

Follow-up controls are necessary for many ultrasound findings (e.g. growth disorders in the baby). Doppler sonography provides information about the progress of the disease and can help in making decisions about whether the due date should be brought forward.

How does Doppler ultrasound work?

The ultrasound head emits ultrasound waves of a specific frequency. If this bundle of sound waves hits the blood cells in the vessels, some of the waves are reflected with a different frequency. The frequency change depends on the movement of the blood cells. The speed and direction of the blood cells change at vascular constrictions. This can be represented in various ways, for example acoustically as tones or color-coded in the ultrasound image. Typically, the flow toward the transducer is shown in red and away from the transducer in blue. This gives the doctor information about the direction and speed of the blood flow. In addition, the course of the blood vessels, the vessel diameter and the condition of the inner layer of the vessel can be assessed.

How is Doppler Ultrasound performed?

In principle, Doppler or duplex sonography of vessels is performed like any other ultrasound examination. A gel is first applied to the appropriate area of ​​skin. This is necessary because the air between the transducer and the skin would otherwise reflect the ultrasound waves. The ultrasound head is guided to the affected body region. If there is a suspicion of a narrowing of an artery supplying the brain, this would be the lateral neck region, for example.

What is examined with the Doppler ultrasound?

The blood flow in the blood vessels of the baby is examined. Particular attention is paid to the aorta and the cerebral vessels. In addition, the blood flow in the placenta, the uterus and the umbilical cord is examined with the Doppler ultrasound. In particular, the following vessels are considered:

• ae Uterinae (uterine artery) : During the examination, two supply areas are examined more closely. The first are the blood vessels that supply the uterus and placenta. Their control is primarily used to predict whether the child will have growth retardation or a maternal blood pressure disorder such as preeclampsia during the course of pregnancyis to be expected. The ideal time for the examination is between the 20th and 24th week. In a normal pregnancy, the vascular supply to the uterus changes over time. The resistance decreases continuously up to the 24th week. If it remains high, your doctor can read this from the course of the curve. In the first half of pregnancy, this phenomenon can also be observed in normal pregnancies. However, in late pregnancy it is always a possible indication of an increased risk of developing a condition such as preeclampsia.
• A. umbilicalis (umbilical cord artery) : The second supply area affects the child and the child’s part of the placenta. The most important vessel is the umbilical artery, which indirectly indicates how the child is supplied via the placenta. This examination is only necessary if there are signs of a child’s disorder, such as growth retardation. The precise assessment of the child’s condition in the event of illness requires the measurement of other child vascular areas, such as cerebral blood flow. It is determined individually. In a normal pregnancythe resistance in the umbilical artery decreases continuously. The normal flow pattern shows blood flow even when the heart is relaxing. An even blood flow is therefore guaranteed. A zigzag curve can be seen on the monitor, which rises sharply and falls somewhat flatter. The peaks indicate the high blood pressure at the beginning of a heartbeat (systole), and the valleys mark the low blood pressure as the heart relaxes and refills (diastole). For disturbances in the placentavascular resistance increases. In severe cases it is even possible that the blood flow in diastole is no longer present or that the blood flow reverses. On the monitor, this is reflected in small gaps that appear between the individual “mountains”. As a result, the blood is partly pushed back and forth in the umbilical cord, which is a great disadvantage for the care of the child. In this case, it is often necessary to give birth prematurely.
• Median cerebral artery (baby’s middle cerebral artery) : Blood flow through the brain is measured in the middle cerebral artery. If the child’s oxygen supply is at risk, the large blood vessels in the brain automatically dilate so that the supply gap can be compensated. A falling vascular resistance of the cerebral artery can therefore indicate a circulatory redistribution. From this point on, the child must be monitored more closely so that the doctor can identify an undersupply in good time. in some cases, for example when it comes to determining the date of delivery, the perfusion in the veins can also be examined.