Ultrasound diagnostics is not the last among the diagnostic procedures adopted in obstetric and gynecological practice. Its use allows timely detection and prevention of the lion's share of pathological abnormalities in the state of the mother and the child in her womb.
Doppler ultrasound during pregnancy allows you to assess the quality of blood flow through the main arteries of the "uterus-placenta-fetus" system, to diagnose existing disorders and failures in a timely manner.
Dopplerography during pregnancy as the main diagnostic procedure
The most complete and reliable information on the dopplerogram can be obtained in the period from the 30th to the 34th week of pregnancy Doppler Data Analysis
A qualified specialist is engaged in deciphering the dopplerogram (blood flow graph), who, highlighting certain areas, calculates relative indices showing vascular resistance and describing the nature of the blood supply in the system of the uteroplacental and placental-fetal vascular bed. And also compares the received data with the established norm.
The most complete data are obtained from a cumulative study of the entire uterine-fetal blood exchange: utero-placental blood flow, placental-fetal blood supply, blood flow through the main vessels of the fetal brain and uterine arteries. Diagnostic criteria for circulatory disorders in the "womb-placenta-fetus" system are:
- slowing down of blood flow in the uterine arteries during diastole;
- deceleration/cessation/reverse flow in the umbilical arteries during diastole.
In severe conditions, such changes are found in the systolic period. The following relative indices are evaluated: systole-diastolic ratio (the ratio of blood flow rates during systole and diastole), resistance index (IR - resistance of the vascular wall), PI (pulsation index).
Deciphering dopplerographic indices, standards
As a result of the research, the average standards of relative indices calculated on the basis of blood flow velocity indicators were derived. They depend on the gestational age.
The standards for LMS are indicated in the table:
The average IR of the aorta of a child in the womb is 0.75. For the middle cerebral artery from 22 weeks to delivery, the IR is 0.773.
Based on the above norms, when deciphering, the degree of circulatory pathology in the "womb-placenta-fetus" system is determined. It also establishes which type (uteroplacental / IPC, placental-fetal / PPC) of the blood flow is disturbed. There are three degrees of circulatory disorders between the uterus and the child in its cavity:
- one of the types of blood flow of the IPC or PPC is disturbed while maintaining the other;
- both types of blood flow are disturbed, but the violations are not critical at the moment and require immediate intervention for correction;
- both types of blood flow (IPC or PPC) are disturbed, the level of violations is critical.
According to the obtained interpretation of the dopplerogram, the obstetrician-gynecologist leading the pregnancy judges the degree of suffering of the child in the womb in a number of pathological processes: a maturing Rhesus conflict, the degree of vascular pathology of the mother and child in her womb with the progression of diabetes mellitus, hypertension or myocardial disease. Also, the doctor has the opportunity to assess the state of the vessels of the fetus during multiple pregnancy, and determine whether the development of one fetus is at the expense of another.
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The moment when a woman first learns about the onset of pregnancy, and the 9 months that follow, is a very exciting and responsible period of time. The health of the unborn child and his mother depends on how well the pregnancy will proceed. In order to timely identify the slightest disturbances in the development of the fetus, as well as determine the position of the fetus in the womb and evaluate its development, during pregnancy, women are prescribed several ultrasound procedures.
All of them are absolutely harmless and do not pose a threat to health. Dopplerometry during pregnancy is one of the options for an ultrasound examination, which gives a more complete picture of the condition of the fetus, helps to determine the causes of deviations and take timely measures to eliminate them.
The principle of operation of ultrasound with a Doppler probe
In medicine, this procedure is called dopplerometry. To understand what it is - dopplerometry for pregnant women, consider the principle of operation of this device. In general, a doppler is a common ultrasound machine that helps to study the blood circulation of the fetus, placenta and reproductive organs of the mother.
The principle of operation of the sensor is based on the Doppler effect. The device generates ultrasonic waves that are reflected from moving particles (erythrocytes) and are captured by the sensitive elements of the device. The screen displays an image of blood flow in the vessels of the uterus, umbilical cord, aorta and cerebral arteries of the fetus in a two-dimensional plane.
This procedure has some differences from conventional ultrasound:
In what cases is a Doppler study prescribed?
In order to avoid complications and irreversible consequences, you need to register in the antenatal clinic as early as possible. The gynecologist observes the condition of the woman and the fetus during all 9 months of pregnancy and prescribes a list of mandatory procedures. The number and types of studies are assigned based on the state of health of the mother, the development of the fetus, as well as the presence of harmful addictions or chronic pathologies.
There are, however, a number of procedures that are prescribed to all women without exception - including Doppler during pregnancy. This study is considered the most informative and important in diagnosing the condition of a woman and a fetus. In the normal course of pregnancy, such an examination is prescribed twice - at 22–24 and at 30–34 weeks. If the gynecologist, during a routine examination of a pregnant woman, reveals a pathology or deviation from the norm, to clarify the clinical picture, he may prescribe an unscheduled Doppler examination.
So, the following conditions are considered indications for repeated Doppler ultrasound during pregnancy:
- diseases of the mother in a chronic course - diabetes mellitus, arterial hypertension, kidney pathology, disorders in the work of the heart and blood vessels, late toxicosis of pregnant women, respiratory failure;
- the presence of urinary tract infections in a woman, large uterine fibroids, severe anemia;
- different Rh factor in mother and fetus;
- multiple pregnancy, oligohydramnios and polyhydramnios, various delays in the development of the fetus in the womb, early maturation of placental tissues;
- pathologies of the woman's health observed during previous pregnancies, in particular late toxicosis in severe course, premature aging of the placenta, as well as fetal death in the womb for various reasons at any time;
- doppler during pregnancy allows you to clarify the results of a planned ultrasound examination in cases of detection of abnormal sizes of the fetal heart, expansion of the heart chambers or failures in the rhythm of the heartbeat;
- the emergence of suspicions about the development of various fetal heart defects or to diagnose its type;
- pathologies in the fetal circulation - determine the type and severity of dysfunction;
- if the child has malformations of the kidneys, organs of the abdominal region or lungs;
- the presence of suspicions about the development of non-cardiac pathologies of the fetus;
- the development of an aneurysm of the vein of Galen, that is, the pathology of a large vessel of the brain, was established;
- entanglement of the umbilical cord around the child's neck with two or more loops;
- vasa previa or the presence of only one artery in the umbilical cord;
- placenta adherent to the walls of the uterus, which will not separate from it spontaneously during childbirth.
If the doctor prescribes the treatment of a particular pathology, then a repeated Doppler ultrasound may also be prescribed to diagnose the results.
Preliminary preparation and procedure for conducting the study
To conduct dopplerometry during pregnancy, a woman does not require any complex preparation, as well as before other planned ultrasound procedures. The difference between dopplerometry and simple ultrasound is that during the examination, a specialist can listen to the child's heartbeat and the noise of blood flowing through the vessels.
There is nothing terrible or dangerous in how dopplerography is done during pregnancy. During the procedure, the woman is offered to lie on her back on the couch and expose her stomach. A special gel is applied to the skin, and an ultrasound sensor is placed on top of it, which reads the information. In most cases, modern equipment has a Doppler function. The examination time usually does not exceed a few minutes.
The specialist to whom the patient was referred for a doppler for pregnant women first of all examines the general condition of the uterus and fetus in order to establish the presence of visible pathologies. After that, the Doppler function is turned on in order to examine in more detail the cardiac aorta, the arteries of the brain and other internal organs of the fetus and the umbilical cord. On the screen, you can see the state of the vessels that are of interest to the doctor at a particular moment. Analysis of the information received by the sensor, the equipment performs in automatic mode. If there are deviations from the norm, this will be visible on the scoreboard of the device.
Varieties of Doppler studies
Depending on the capabilities of the device, doppler during pregnancy is carried out in duplex or triplex mode. With a duplex examination on the screen, you can examine the vessel, assess the degree of its patency and, in case of pathologies, detect their causes. When using the triplex mode, a color image is displayed on the screen, which shows the movement of red blood cells in the vessels. In this regard, the triplex version of the study is considered more accurate and informative.
Will dopplerometry hurt a child?
There is no need to be afraid of a Doppler study during pregnancy - it will not bring any harm to either the mother or her unborn child. On the contrary, this type of diagnosis makes it possible to prevent the development of many pathologies and to carry out treatment in time if deviations from the norm were found. In particular, with the help of Doppler ultrasound during pregnancy, you can see the entanglement of the fetus with the umbilical cord, determine its degree (tight or not, single, double, triple), as well as identify the onset of fetal hypoxia and take measures to eliminate it.
In any case, it is better for pregnant women to remain calm and not worry over trifles. It is desirable to pay attention to the observance of the diet, sleep and rest, getting rid of bad habits, if any.
Deciphering the results
To decipher dopplerometry during pregnancy, experts use special indices. So, to assess the quality of blood circulation, such indices are used as the ratio of blood flow rates during the period of contraction (systole) and relaxation (diastole). First, the highest point is marked on the graph - this is the highest blood flow velocity during ventricular contraction. Then find the lowest point - this is the final speed in diastole. After that, the average blood flow velocity for one cardiac cycle is calculated. Next, the device calculates a number of indices that allow you to evaluate the spectrum of blood flow: pulsation (PI), resistance (IR) and systole-diastolic ratio (SDO).
The normative indicators of dopplerometry for pregnant women are indicated in special tables, with which the specialist will compare the results and draw conclusions about the absence or presence of deviations, as well as possible consequences. The most common causes of circulatory disorders in the fetus are arterial hypertension and severe late toxicosis in a woman.
Doppler during pregnancy makes it possible to evaluate such criteria for blood flow disorders between the placenta and the uterus, such as:
- decrease in diastolic velocity below normal;
- an increase in the resistance index in the arteries of the uterus;
- the occurrence of an early diastolic notch in the blood flow velocity in the uterine arteries.
The presence of disturbances in the blood circulation between the placenta and the fetus is evidenced primarily by a decrease in the blood flow velocity in the arteries of the umbilical cord and an increase in the resistance index above the norm for a given gestational age.
Artifacts during a Doppler study
Of course, no electronics can always work perfectly, including an ultrasound machine. Often, distortion or artifacts may appear on the screen. These are extraneous geometric structures that differ from the real prototypes in shape and size. When conducting Doppler during pregnancy to study blood circulation in triplex mode, a specialist sometimes finds artifacts that can affect the correct interpretation.
Most often you can see such artifacts:
- weak staining, i.e. failures in color display when the vessel is deep, the scanning angle is incorrect, or the device settings are incorrect;
- pseudo-flow image, that is, erroneous staining of any fluids, urine, amniotic fluid;
- image failures when the device frequency settings and blood flow velocity do not match;
- flashes of color when the sensor moves too quickly or the movement of extravascular formations - bowel contractions, air movement;
- flickering, that is, the formation of a reflective color path - metal fragments, stones.
In any case, qualified doctors are aware of the possibility of such artifacts, so they can distinguish them from real pathologies.
The Doppler effect in the case of a medical study is that ultrasonic waves are reflected from blood particles, and this change will directly depend on the blood flow velocity. Ultrasound with a special sensor is used to assess blood flow through the main vessels (arteries, veins) of the neck, arms, legs. The study can reveal difficulties in blood flow during vasoconstriction, detect blood clots in the veins.
To assess blood circulation in the vessels of the brain, this study is used in the following cases: to determine the risk of stroke, cerebrovascular accident, vasospasm, after coronary artery bypass grafting (to determine the likelihood of embolism), as well as in neurosurgical patients. Indications for Doppler ultrasound are: migraines, dizziness, vegetative-vascular dystonia, headaches of unknown origin.
Doppler of the vessels of the neck reveals the pathology of the vertebral and carotid arteries. This study is used for the following symptoms: noise in the head, transient ischemic attacks with temporary paralysis of half of the body or arm, dizziness, temporary blindness in one eye, flickering before the eyes, short-term loss of consciousness, headaches, temporary imbalance, falls, not accompanied by loss consciousness.
Ultrasound examination of the vessels of the lower extremities reveals the pathology of the arteries and veins. It is performed with the following symptoms and diseases: pathology of the arteries and veins of the lower extremities, intermittent claudication, hypersensitivity of the legs to cold, chilliness, numbness in the feet, varicose veins, swelling of the legs, heaviness in the legs, pigmentation of the skin on the legs.
Doppler ultrasound during pregnancy
Doppler ultrasound is prescribed during pregnancy to determine the rate of fetal blood flow in order to assess the functioning of the placenta. This study is carried out if there are concerns about the intrauterine growth of the child, as well as with an increase in blood pressure in a woman. A cardiotocograph (a special type of Doppler) is used to evaluate the fetal heartbeat. If a pregnant woman regularly feels the movements of the baby, most likely this study will not be prescribed.
The fetus is connected to the placenta through the umbilical cord, 2 arteries and 1 vein pass through it. The placenta delivers nutrients and oxygen to the baby through the blood. If blood flow is obstructed, the fetus may not get enough of them, which can cause growth retardation. In case of detection of high resistance to blood flow through the vessels, the question of early delivery may arise.
A large number of studies that a woman undergoes during pregnancy is fully justified, since the modern rhythm of life leaves a certain imprint, often negatively affecting the formation and development of the fetus. This is confirmed by the ever-increasing percentage of complications during pregnancy.
The central place among all types of diagnostics used to study and monitor the development of the fetus is occupied by echographic research methods, including:
- classical ultrasound;
- 3D ultrasound;
- screening ultrasound;
- dopplerography.
What information doppler ultrasound results carry during pregnancy and what it is, you can find out by familiarizing yourself with the basic concepts of the principles on which the receipt of information during dopplerography is based, as well as the effect of placental circulation on the full development of the fetus.
The principle of operation of dopplerography
Unlike the use of ultrasound in classical ultrasound, where ultrasonic waves with varying degrees of intensity are reflected from stationary objects, making it possible to assess the uniformity of their internal structure, density and structure, Dopplerography allows you to “see” a moving medium. This property of ultrasound is based on the effect discovered by Doppler back in the 1950s, the essence of which is to evaluate changes in reflected ultrasonic vibrations from moving and stationary structures.
Taking into account that all organic structures have different degrees of acoustic resistance, that is, they reflect ultrasound received by an ultrasound sensor with different degrees of intensity, a vessel filled with moving blood divides identical ultrasonic pulses into two types:
- equal to the initial frequency of ultrasonic waves generated and perceived by the sensor. Such waves make it possible to designate the contour of the vessel, since the vessel is a stationary object;
- reduced or increased frequencies of ultrasonic waves relative to those originally emitted. The frequency change occurs in a mobile medium, that is, in the blood filling the vessel.
A vessel coded in red on the image means that the blood flow is directed towards the sensor, and in blue - away from it
When blood cells (erythrocytes) move in the direction of the source of ultrasonic waves, their surface more often reflects ultrasonic pulses, which causes an increase in the reflected frequency relative to the initial one, the movement of blood flow from the source of radiation, on the contrary, reduces the frequency of reflected pulses. This phenomenon is called the Doppler shift, in the first case it will have a positive value, and in the second it will be negative.
Important! Erythrocytes located closer to the vessel wall move much more slowly than those in the center. The difference in blood flow velocity is called the velocity profile.
Uteroplacental system
The placenta is a temporary organ that provides the relationship between the mother's body and the developing fetus. The main functions of the placenta are:
- delivery of nutrients to the fetus;
- providing oxygen;
- excretion of end products of metabolism and carbon dioxide;
- protection against the ingestion of toxic substances and drugs into the child's body;
- the synthesis of hormones that support the normal development of pregnancy.
The main criterion for the full functioning of the placenta is the appropriate state of blood flow in the uteroplacental system. Any changes in blood flow in the uteroplacental system, detected using Doppler ultrasound (USDG), can be considered the beginning of the development of pathological disorders in the development of the fetus.
In order to understand what uteroplacental blood flow (MPC) is and what its significance is in ensuring the full development of the child, it is necessary to track the relationship between the timely formation of placental vessels formed from small arterioles and the growing needs of the embryo, which requires the delivery of blood volume, in 10 times greater than their original needs.
The final restructuring of small arterioles ends by the beginning of the third trimester (20-24 weeks). At this point, the vessels are thick enough to allow a large amount of blood to circulate due to their low resistance. Delay or disruption of the formation of full-fledged arteries causes an increase in resistance, which leads to impaired blood flow.
Indications
How long to conduct an ultrasound scan depends on the risk of complications in a woman or child. It is advisable to carry out the first Doppler ultrasound during pregnancy after the final formation of the circulatory system, that is, at 20-24 weeks of pregnancy.
It is advisable to conduct a study at these times in patients at risk of developing the following complications:
- preeclampsia;
- chronic kidney disease;
- hypertension;
- endocrine disorders;
- vascular disorders;
- aggravated history (repeated early termination of pregnancy);
- abnormal placentation in the presence of fibroids or a scar in the area of placental formation;
- delayed fetal development;
- Rhesus conflict between mother and fetus;
- oxygen starvation of the fetus;
- multiple pregnancy.
UZDG of the fetus at 20-24 weeks of gestation not only allows you to identify circulatory disorders in the circle "mother → placenta → fetus", but also, as far as possible, correct the violations that have arisen with the help of timely therapy.
Important! Dopplerography of the fetus should be present as a mandatory component when conducting a comprehensive study at 30-34 weeks of gestation.
The picture shows the veins and arteries of the umbilical cord, that is, the inflow and outflow of blood through the main vessels
Analysis of results
Dopplerography during pregnancy includes not only the study of blood circulation in the circle "mother → placenta → fetus", that is, the movement of blood in the vessels of the uterus and umbilical cord, but also the blood flow in the main arteries of the fetus:
- aorta;
- cerebral blood supply;
- renal arteries;
- venous vessels.
When performing an ultrasound scan, the monitor shows a schematic image of changes in the speed of blood movement throughout the entire cardiac cycle. The graph is a curve with two or three phases, where the highest level reflects the speed of blood flow at the moment of heart contraction (systolic speed), and the lowest level reflects the speed at rest of the heart muscle (diastolic speed). On this graph, you can see the typical curves for each individual vessel.
For a full assessment of the state of blood flow, it is not the speed indicators that are of decisive importance, but the coefficients (indices) that reflect the ratio between systolic and diastolic velocities. In practice, the following coefficients are used:
SDI (SDO) is the systolic-diastolic ratio calculated by the formula: SDI = MaxS/MinD , where MaxS is the maximum systolic blood flow rate, and MinD is the minimum diastolic blood flow rate.
Table: Norms of change in the quantitative indicator of SDI in accordance with the gestational age
| terms of pregnancy,
weeks | Types of arteries |
||
| Aorta | mother | Umbilical cord |
|
| 20-24 | 5,40-6,50 | 1,54-2,25 | 3,80-3,95 |
| 25-28 | 4,99-6,39 | 1,51-2,19 | 2,79-3,59 |
| 29-31 | 4,88-5,94 | 1,48-2,08 | 2,42-3,34 |
| 32-36 | 4,58-5,90 | 1,39-1,99 | 2,21-2,83 |
| 37-41 | 4,50-5,38 | 1,35-1,90 | 1,90-2,38 |
РI (PI) – pulsation index, calculated by the formula: РI = (MaxS- MinD)/SDN, where SDN – average blood velocity. The pulsation index in the uterine arteries should normally be in the range from 0.4 to 0.65.
RI(IR) – resistance index calculated by the formula: RI = (MaxS- MinD)/MaxS .
Table: Norms of change in the quantitative indicator RI in accordance with the terms of pregnancy
| Terms of pregnancy (in number weeks ) | Types of arteries |
||
| Aorta | mother | Umbilical cord |
|
| 20-24 | about 0.75 | 0,34-0,65 | 0,60-0,81 |
| 25-28 | 0,33-0,63 | 0,56-0,77 |
|
| 29-31 | 0,33-0,61 | 0,52-0,74 |
|
| 32-36 | 0,33-0,59 | 0,48-0,70 |
|
| 37-41 | 0,32-0,57 | 0,40-0,67 |
|
However, informative is not only the assessment of quantitative changes in fetal ultrasound, but also a visual assessment of changes in the curves that occur during the development of pathologies. Each individual vessel, depending on the gestational age, should have a characteristic view only for it, therefore, any deformation of the curve (the appearance of a dicrotic notch, insufficient or excessive severity of diastole or reverse blood flow) indicates the development of pathological changes in provisional organs caused by the following conditions:
- fetal hypoxia;
- preeclampsia;
- fetal development disorders at the chromosomal level.
Table: Signs of abnormal pregnancy based on changes in SDI and RI
| Pathology | Indicators |
| Fetal hypoxia, developmental delay | ExcessSDI and R.I. in the uterine arteries |
| Fetoplacental insufficiency, preeclampsia | ExcessSDI and R.I. in the umbilical arteries |
| Transfusion syndrome | ExcessSDI and R.I. in the umbilical arteries in one of the embryos in a multiple pregnancy |
| Post-term pregnancy, endocrine diseases of a pregnant woman (diabetes mellitus), Rhesus conflict | ExcessSDI and R.I. in the aorta |
| Lack of sufficient blood supply to the fetus, defective fetal development | declineSDI and R.I. in the carotid and cerebral arteries of the fetus |
Exceeding the SDI and RI indicators indicates an increase in resistance in the conducting arteries, which, in turn, causes obstructed blood flow and malnutrition of the fetus.
Preparation and holding
Conducting ultrasound during pregnancy does not require any preliminary preparation. If necessary, you can take a disposable diaper and wipes to remove the gel for the procedure. The patient should lie on the couch and expose the abdomen. The further procedure is practically no different from a conventional ultrasound, with the only difference being that during the examination, the doctor performs a scan in two modes:
- conventional ultrasonic;
- dopplerographic.
How is dopplerography done? Almost all modern devices used for ultrasound diagnostics are capable of performing dopplerometry. To do this, the ultrasound machine provides not only a sensor that combines two functions, but also the corresponding software that processes the data and provides information in the form of a color picture (triplex scanning), graphics or digital data.
Dopplerography
With ultrasound of the fetus, the doctor conducts a preliminary study in the echo-scanning mode to determine the position of the fetus, the localization of the placenta and umbilical cord. Having determined the direction of the desired artery, he switches on the Doppler mode, after which he can visually assess the state of blood flow reflected on the monitor and receive a hardware analysis of the examination results.
Harm and restrictions
Ultrasound diagnostics, due to its high information content and the absence of obvious negative effects on the body, which is especially important during pregnancy, is becoming more widespread. However, functions that require the use of increasingly powerful radiation, including Doppler, make the issue of safety more acute.
Although there are no confirmed data on the dangers of ultrasound used for diagnostic purposes, its ability to damage tissues by heating or cavitation cannot be denied. In this regard, the use of Doppler ultrasound during pregnancy is carried out on the principle of "as little as possible." In addition, modern ultrasound diagnostic equipment is equipped with control functions that evaluate the intensity and duration of exposure to ultrasonic waves on the body, in particular, the degree of heating (thermal index) and the likelihood of cavitation (mechanical index).
However, the practical value of Doppler ultrasound in prenatal diagnosis, as well as the ability to predict probable complications in the development of pregnancy, is a decisive argument in favor of using this method.
Doppler ultrasound during pregnancy registers blood flow in the arteries that communicate in the system of the female body between the placental membrane and the fetus. The study is most effective in diagnosing a baby's developmental delay and allows you to choose the appropriate drug therapy; emergency delivery is often recommended.
When and how do doppler ultrasound during pregnancy
Doppler ultrasound during pregnancy is such an examination that records blood flow data in the vessels that communicate between a woman and a child.Modern ultrasound diagnostic devices are already equipped with additional functionality in order to simultaneously conduct ultrasound with Doppler. Thus, during the study, the ultrasound machine on the monitor shows a graph of blood circulation in color. The technique is similar to a standard examination, when waves are reflected from the tissue structure of the body, but with the Doppler effect, the reflection occurs from blood erythrocytes, which provides a complete description of the blood flow in the arteries of the uterine cavity and the fetal brain, in the umbilical cord, and also in the venous duct.
Mandatory dopplerography during pregnancy is used twice. Often, studies are combined - ultrasound plus Doppler, so the timing is the same, which allows you to assess the condition of the mother and baby in the complex at the following stages of development:
- 21 - 24 weeks;
- 30 - 33 weeks.
Doppler ultrasound during pregnancy is prescribed more times if the doctor has serious concerns that a pathological process is developing inside the womb. Basically, among these indications are:
- women smoking;
- kidney failure;
- the presence of high blood pressure;
- multiple gestation;
- diagnosing Rhesus conflict.
.
Doppler norms by week of pregnancy: table
Doppler ultrasound usually begins with the study of blood flow between the two uterine arteries and the placental organ, since in more than 70% of cases, circulatory disorders are observed exclusively on one side with preeclampsia. When studying, indicators of systole (contraction of the ventricles of the heart) and diastole (interval relaxation of the heart in the interval of contractions) are measured.The norms for weeks of gestation contain the following indicators:
- The resistance index, or IR for short, is calculated using the formula (C - D) / C, while studying the difference between systolic and diastolic velocities, which are divided by the final diastolic;
- The systolic-distal ratio (SDR) refers to the index between maximum contraction speed and highest relaxation speed (S/D);
- The pulsation index (PI) is used to estimate the pulsation rate, the difference between the velocities is calculated divided by the average blood flow data (S - D) / M).
| Vessel | Index | 28 weeks | 32 weeks | 36 weeks | 40 weeks |
|---|---|---|---|---|---|
| umbilical artery | FROM TO | 3,1-3,7 | 2,8-3,4 | 2,4-3,0 | 2,2-2,5 |
| IR | 0,65-0,73 | 0,60-0,67 | 0,55-0,63 | 0,51-0,59 | |
| PI | 1,08-1,09 | 0,95-0,96 | 0,83-0,84 | 0,73-0,74 | |
| fetal aorta | FROM TO | 6,0-7,6 | 5,7-7,3 | 5,4-7,1 | 5,2-6,8 |
| IR | 0,82-0,88 | 0,80-0,86 | 0,77-0,83 | 0,75-0,81 | |
| PI | 1,79-2,24 | 1,76-2,20 | 1,74-2,17 | 1,72-2,13 | |
| internal carotid artery | FROM TO | 5,6-6,5 | 4,7-5,6 | 4,0-4,8 | 3,3-4,1 |
| IR | 0,78-0,88 | 0,74-0,84 | 0,71-0,81 | 0,69-0,78 | |
| PI | 1,98-2,39 | 1,70-2,06 | 1,44-1,77 | 1,22-1,51 | |
| Uterine artery | FROM TO | 1,7-1,9 | 1,7-1,9 | 1,7-1,9 | 1,7-1,9 |
| IR | 0,46-0,55 | 0,69-0,86 | 0,69-0,86 | 0,69-0,86 | |
| PI | 0,69-0,86 | 0,69-0,86 | 0,69-0,86 | 0,69-0,86 |
