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24MEDICAL SCIENCES
MODERN VIEW ON ULTRASOUND DIAGNOSTICS IN OBSTETRICS
Shepetovskaya N.
Sechenovsky University, Moscow, Senior Lecturer, Ph.D.
Kalenteva S.
Medical League of Russia, Moscow, Prof., Ph.D., M.D.
Shepetovskaya M.
Sechenovsky University, Moscow, Student, Faculty of Medicine
ABSTRACT
The article provides a review of the modern literature on the use of ultrasound diagnostics in obstetrics and its effectiveness in different trimesters of pregnancy, during childbirth and the postpartum period.
Ultrasound is a non-invasive method that does not create radiation exposure, which is an ideal imaging method during pregnancy. Modern technologies and techniques include abdominal and transvaginal 2D scanning, M-mode imaging, Doppler and color Doppler mapping, energy color Doppler imaging, and 3D ultrasound.
To date, ultrasound diagnostics continues to actively develop and improve.
Keywords: ultrasound diagnostics, dopplerography, trimester of pregnancy, childbirth, the postpartum period, obstetrics.
Modern advances in clinical diagnostics are largely determined by the improvement of research methods. Significant progress in this area has been achieved thanks to the development and implementation of fundamentally new methods of obtaining medical images, including the ultrasound method.
Ultrasound is a non-invasive method that does not create radiation exposure, which is an ideal imaging method during pregnancy. Due to the evolutionary improvement of ultrasound technologies in recent years, there are now a number of unique methods of ultrasound examination, the use of which depends on the duration of pregnancy and the purpose of the study. Modern technologies and techniques include abdominal and transvaginal 2D scanning, M-mode imaging, Doppler and color Doppler mapping, energy color Doppler imaging, and 3D ultrasound.
The use of ultrasound diagnostics in obstetrics and gynecology begins in 1966, when in Europe, the United States and Japan actively began to apply ultrasound diagnostics in this specialty. Both a - and b-modes were used, including the first "fast b-scanner", the Vidoson ® from Siemens ®, used by D. Hofmann and Hans Holländer at the Wilhelm University in Munster, Germany [18].
Ultrasound examination in obstetric practice is the most important diagnostic tool that allows you to identify a wide range of different pathologies in early pregnancy, such as undeveloped and ectopic pregnancy [8], fetal malformations [2, 21]. To assess the rate of fetal development, to predict and prevent a number of obstetric syndromes, such as fetal growth retardation [48], preeclampsia [37], preterm birth [6], antenatal fetal death [1].
The main tasks of ultrasound examination in obstetrics [3]:
- establishing the fact of pregnancy, monitoring its course;
- determination of the number of fetal eggs;
- embriometry and fetometry;
- diagnosis of fetal abnormalities;
- evaluation of the functional state of the fetus;
- placentography;
- implementation of control during invasive studies.
Ultrasound examination in the first trimester of pregnancy
The purpose of ultrasound in the first trimester of pregnancy [7, 43]:
- to establish the presence of uterine pregnancy on the basis of visualization of the fetal egg in the uterine cavity;
- with the exception of ectopic pregnancy;
- diagnosis of multiple pregnancies;
- evaluation of fetal egg growth (average internal diameter of the fetal egg, coccygeal-parietal size and biparietal size of the embryo/fetus);
- assessment of the vital activity of the embryo (cardiac activity and motor activity);
- study of the anatomy of the embryo/ fetus. Detection of chromosomal abnormalities ecomercio;
- study of extraembryonic structures (yolk sac, amnion, chorion, umbilical cord);
- diagnosis of pregnancy complications (threatened/initiated / complete abortion, cystic drift);
- diagnosis of genital pathology (uterine fibroids, uterine abnormalities, intrauterine pathology, ovarian formations).
However, the use of ultrasound screening in the first trimester of pregnancy up to 10 weeks is impractical and should be carried out according to strict indications, since it is impossible to completely exclude the possible adverse effects of ultrasound on the processes of embryogenesis and the development of pregnancy in general [30]. Indications for an emergency immediate examination in early pregnancy include [3]: • pain in the lower abdomen, especially in the presence of risk factors for ectopic pregnancy in patients who have not yet undergone ultrasound; • massive bleeding; • systemic symptoms of blood loss.
In the first trimester of pregnancy, transvaginal ultrasound is mainly used. One of its advantages is that it does not require a full bladder when examined. It also provides a higher image resolution compared to the abdominal one. This is especially important in pregnant women with retroflexia of the uterus. However, there are also disadvantages. One of them is that transvaginal ultrasound shows the pelvic organs in a projection different from the abdominal one. In addition, it has limited scanning capabilities for higher-placed structures [29].
The first sign that the patient may be pregnant is the presence of an eccentrically located small cyst within one layer of the endometrium. Soon, other signs also appear, such as the "double bleb sign" symptom, the presence of a yolk sac, and then the echogenic cylinder, which is the embryonic pole. The echogenic rim around the fetal egg in the early stages of development is a decidual reaction [7].
During the first screening ultrasound (10-14 weeks), it is important to diagnose a number of severe fetal malformations (anencephaly, acrania, some limb malformations, etc.) [24, 30]. One of the most common developmental abnormalities is congenital heart disease (CHD) [23]. However, the sensitivity of echogra-phy in the diagnosis of congenital heart defects at the first screening level does not exceed 30% and a high frequency of false-positive results is noted [7].
Biometrics in the early stages of uncomplicated pregnancy can be limited to measuring the average internal diameter of the fetal egg and the coccygeal-pari-etal size of the embryo. The error in determining the term of pregnancy in the first trimester can be minimized if the rules of biometrics are strictly followed [30, 43]. After that, it is necessary to evaluate the signs of vital activity of the embryo, which include cardiac activity (recorded from the beginning of week 6) and motor activity (determined after week 7).
It is important to assess the condition of the internal pharynx and cervix at an early stage, since isthmic-cervical insufficiency can be the cause of termination of pregnancy [30]. Another risk factor for preterm birth may be the presence of uterine abnormalities in a pregnant woman [28] and this is associated with a short length of the cervix [26].
Predictors of pregnancy pathology in the early stages of pregnancy are the absence of fetal cardiac activity, calcification of the yolk sac, etc. [7].
The absence of a heartbeat of the embryo / fetus is considered a sign of death, but it should be remembered that in a very small embryo (<4 mm), heart contractions may not be detected, so ultrasound should be performed again after a few days. The value of the embryo length of 5 mm is a threshold value detected during ultrasound examination, in which cardiac activity should be visualized in all cases [7].
Ultrasound examination in the second trimester of pregnancy
The purpose of ultrasound in the second trimester of pregnancy [3, 43]:
- оценка роста плода;
- диагностика пороков развития;
- исследование маркёров хромосомной патологии;
- диагностика ранних форм задержки развития плода;
- оценка локализации, толщины и структуры плаценты;
- определение количества околоплодных вод.
During this time, ultrasound examination makes it
possible to diagnose most of the congenital malformations of the fetus. However, not all of them. This may be due to the following reasons. First, some malformations may appear later in pregnancy, or they are diagnosed only in the third trimester of pregnancy. Secondly, the quality of prenatal diagnostics is significantly affected by the capabilities and resolution of ultrasound devices [30].
The spectrum of echomarkers of fetal chromosomal pathology detected in the second trimester of pregnancy includes changes in various organs and systems: ventriculomegaly, cysts of the vascular plexuses of the lateral ventricles, abnormal forms of the skull and cerebellum ("strawberry", "lemon", "banana"), hyperecho-genic intestine, pyelectasia, a single umbilical cord artery, a symmetrical form of fetal development delay [3].
As part of the diagnosis of intrauterine growth retardation, it is important to determine the size of the fetus 'head, since when the fetus' development is delayed, its brain continues to grow, despite the fact that the development of other parts of the body slows down. To improve the effectiveness of the diagnosis, it is necessary to use additional parameters when measuring the fetal head, trunk (the average diameter of the chest), fetal limbs (the length of the radius and ulna, the width of the scapula, the length of the foot). The determination of the estimated fetal weight in the diagnosis of intrau-terine growth retardation is also of great practical importance. The calculation of the expected fetal weight is carried out on the basis of fetometry. For this purpose, the use of various formulas is proposed [30, 43].
In assessing the nature of the course of pregnancy, it is essential to determine the volume of amniotic fluid, which is an integral part of the antenatal ultrasound examination and serves as a diagnostic test for identifying pregnant women at high risk for the development of perinatal pathology [29]. A decrease in amniotic fluid to 500 ml or less (at the end of pregnancy) is considered low water, and an increase of more than 1500 ml is considered polyhydramnios. Low water content occurs in the second and third trimesters, and high water content occurs in the third trimester [43]. A significant tortuosity of the amnion indicates an excessive number of active-secreting amniocytes. In some observations with polyhydramnios, thickening and compaction of the compact layer was revealed, which leads to blocking of water resorption. In the course of the study, not only the fact of an abnormal amount of amniotic fluid is recorded, but also the degree of severity of this pathology, despite the significant element of subjectivity of such a diagnosis. Estimation of the volume of amniotic fluid during an echographic examination is possible by determining the average diameter of randomly selected free spaces ("pockets") filled with water. The volume
of ocular water is considered normal if the average diameter of the "pockets" is within 2-8 cm. Polyhydramnios are characterized by the size of "pockets" of more than 8 cm, and low-water-less than 2 cm. The presence of a free "pocket" of less than 1 cm in size is taken as a pronounced lack of water [30, 43].
With the help of ultrasound in these terms, you can study the placenta in detail and get the necessary information about its localization, thickness, and structure [29, 30].
The location of the placenta in different periods of pregnancy changes due to the "migration" from the lower segment to the bottom of the uterus. If a placenta previa is detected before 20 weeks of pregnancy, the ultrasound should be repeated every 4 weeks. The final conclusion about the location of the placenta should be made at the end of pregnancy.
Information about the state of the placenta can be obtained by placentometry [3, 30]. Most often, the thickness of the placenta is determined, since this measurement is the most accurate and simple. The determination of the area and volume of the placenta due to the complexity of the technique is not widely used in the diagnosis and is used only in individual cases.
During the physiological development of pregnancy, the thickness of the placenta continues to increase until the term of 35-36 weeks and then decreases slightly, amounting to an average of 3.4 cm in the paracentral part at the time of delivery [3]. The size of the placenta may vary depending on the existing pathology, the severity and duration of the process. An increase in the thickness of the placenta is often detected with iso-serological incompatibility of the blood of the mother and fetus, diabetes mellitus, non-immune dropsy of the fetus, the presence of a large fetus. With the threat of termination of pregnancy, gestosis, delayed intrauterine development of the fetus, some malformations and low water content, most often there is a decrease in the size and thinning of the placenta [29, 30].
During pregnancy, changes in the echographic structure of the placenta occur, which are mainly due to involutive-dystrophic processes [30].
With the help of ultrasound examination of the placenta, it is possible to diagnose such a terrible complication of pregnancy as placental abruption, which is a consequence of a violation of the mechanisms of its attachment to the wall of the uterus, followed by bleeding from the vessels of the decidual membrane. Ultrasound diagnosis of premature placental abruption is based on the detection of the echonegative space between the uterine wall and the placenta. The size of the hematomas is of great importance. The echographic image of hematomas varies depending on the age of their existence [30, 43].
Ultrasound is also used to diagnose the consistency of the postoperative scar on the uterus. This condition is associated with a high risk of uterine rupture with the progression of pregnancy and massive bleeding [39]. The consistency of the scar is evidenced by the homogeneous structure of the tissues and the smooth contours of the lower segment of the uterus, its thickness is not less than 3 -4 mm. The failure of the scar on the uterus is diagnosed based on the detection of a
defect in the form of a deep niche, thinning in the area of the alleged scar, the presence of a large number of hyperechoic inclusions (connective tissue) [30].
Patients with a scar on the uterus after cesarean section and with low placentation (presentation) of the placenta in the second trimester of pregnancy are considered to be at high risk for placental increment [44, 20].
Ultrasound examination in the third trimester of pregnancy
The purpose of ultrasound in the third trimester of pregnancy [3, 43]:
- diagnosis of malformations with late manifestation;
- determination of fetal developmental delay;
- assessment of the functional state of the fetus (assessment of motor and respiratory activity, Doppler blood flow in the "mother-placenta-fetus" system).
The main purpose of this screening is to identify placental dysfunction (intrauterine development delay, lack of water, pathological form of velocity waves in the Doppler study) [35, 40].
When studying the growth and development of the fetus in the second and third trimesters of pregnancy, fetometry is performed. Fetometry is a required component of ultrasound in obstetric practice and allows you to set according to the size of the fetus in pregnancy and to assess its growth, to clarify the term of pregnancy, to diagnose fetal growth retardation and congenital malformations [29, 30].
The mandatory volume of fetometry includes the measurement of the biparietal size and circumference of the head, the diameter or circumference of the abdomen, and the length of the femur (the length of the tubular bones is measured on both sides). There are tabular values of standard gestational indicators of fetometry. Based on these parameters, it is possible to determine the estimated weight of the fetus [3, 30].
If one or more of the main fetometric indicators are found to be inconsistent with the gestational age, extended fetometry is necessary [30].
Another important indicator is the assessment of the degree of maturity of the placenta according to the classification proposed by P. A. Grannum et al. (1979). Based on the echographic characteristics of the chorial plate, placental parenchyma, and basal layer, depending on the gestation period, four degrees of placental maturity are distinguished: 0, I, II, and III. In the physiological course of pregnancy, structural changes in the placenta occur in parallel with the development and maturation of the fetus [29, 30].
A number of other characteristics of the placenta that may have pathological signs deserve attention: additional pathological inclusions in the structure of the placenta, its thickness and location
Ultrasound scanning reveals pictures of cystic changes, a sign of which are echonegative formations of various sizes. However, true placental cysts are rare. Large cysts can contribute to the development of atrophic processes in the placenta due to compression of the surrounding tissues, which adversely affects the development of the fetus. The presence of multiple
small cysts can also negatively affect the function of the placenta [7].
Another important obstetric problem is pathological placentation (placenta previa and placenta accreta) [25]. Antenatal diagnosis is determined by a combination of anamnestic, clinical, and instrumental data. The leading role among instrumental research methods is assigned to ultrasound diagnostics [44, 20]. However, Z. S. Bowman et al. [9] in their study, they found that the sensitivity of the method is only 53% and the specificity is 88%, that is, in every second pregnant woman, the diagnosis of placental ingrowth is not confirmed by ultrasound data.
True placental increment, which is extremely rare, is a serious complication. The echographic picture with a true increment of the placenta in cases of its presentation is characterized by the presence of multiple hy-poechoic formations between the area of the internal pharynx and the placental tissue, which are embedded in the myometrium. A great help in the diagnosis of this pathology is provided by the Doppler study, which reveals the penetration of placental vessels into the my-ometrium [12, 30].
With the help of ultrasound, you get valuable information about the state of the cervix during pregnancy and about the risk of premature birth. Transvaginal echography has now become an almost non-alternative method of investigation used to assess the condition of the cervical canal and internal pharynx [16]. It has 100% sensitivity and 80% specificity. According to the 2015 FIGO recommendations [25], the length of the cervical canal with transvaginal ultrasound cervicometry of 35 mm or less indicates a threat of preterm birth, 25 mm or less-a high risk of direct preterm birth. The expansion of the internal pharynx to 5 mm or more, especially to 10 mm, also indicates a high risk of premature birth.
Using ultrasound cervicometry, the existence of a latent and active period of labor is clearly confirmed. It was found that with the onset of labor, there is a transformation of the cervix: its shortening with increasing thickness. The smoothing process is carried out sequentially in four stages [10]: T-stage (when the cervix is formed and does not differ from that in the last weeks of pregnancy), Y -, V-stage and U-stage (corresponding to the complete smoothing of the cervix). In cases of induction of labor by oxytocin, cervical smoothing occurred in the same way, but in a shorter time. Echogra-phy data did not reveal any difference in the mechanism of cervical smoothing between first-and second-born women, i.e. smoothing in all cases precedes disclosure, which differs from the results of a bimanual study.
Ultrasound examinations during childbirth
In classical obstetrics, to assess labor, determine the type and position of the fetus, the location of its head, as well as to decide on the timing and method of surgical intervention, the doctor is traditionally guided by the data obtained during the vaginal examination. This approach, of course, remains fundamental, although its inherent subjective nature cannot be denied.
The use of echography during labor was previously insignificant and was mainly used for cephalom-etry when planning labor. This was due to the high cost
of ultrasound machines and the inability to have an ultrasound machine in every delivery room. In recent years, with the development and cheapening of ultrasound technologies in the world, there has been a rapid introduction of diagnostic ultrasound in childbirth. As at the time the ultrasound is a revolution in the antenatal surveillance, as is happening now and in the management of labor. This approach is non-invasive, provides real-time results, and allows you to instantly make a decision in a critical situation [22, 45].
Ultrasound examination in childbirth aims to assess the progress of the fetal head through the bone ring of the pelvis, to show the possibility of natural delivery in this particular case, or to give a reliable conclusion about the need for surgical intervention. During ultrasound examination in childbirth, transperineal access is used. Currently, several methods of transperineal ultrasound examination in the second period of labor have been developed in the world in order to assess the progress of the fetal head. One of the most accessible and informative is the progression angle [45]. It represents the angle between the long axis of the pubic joint and the line drawn from the lower edge of the symphysis along the lowest point of the bony structures of the fetal head. This parameter, first proposed in 2009, allows for fairly accurate determination of the head's progress in the pelvic cavity [13, 31, 33].
Extensor options for inserting the fetal head can be excluded in the longitudinal scan, when the fetal chin is pressed against the chest. The clinical diagnosis is made on the basis of palpation of sutures, fontanelles and determination of bone landmarks of the pelvis of the mother, but the use of ultrasound improves the diagnosis of these abnormalities in childbirth [4]. At the same time, according to Sherer D. M. (2002) et al., when comparing the data of ultrasound and vaginal studies to determine the position of the fetal head, the error rate reaches 76% [41, 42].
The combination of transabdominal and transper-ineal studies allows the most accurate diagnosis of syn-clitic and asynclitic insertions, flexor and extensor positions of the fetal head [5].
Transperineal ultrasound examination in the second period of labor is highly informative for assessing the progress of the fetal head. Proper evaluation of the results allows you to reduce the number of unnecessary caesarean sections. On the other hand, in the presence of a birth tumor in the fetus, ultrasound with the measurement of the angle of progression makes it possible to make the right timely decision in favor of a cesarean section. The preservation of echograms in electronic form and on paper allows you to document the decisions made in terms of changing the tactics of labor management [14].
The use of ultrasound in childbirth improves the diagnosis of incorrect positions of the fetal head, contributes to the prevention of complications from the mother and fetus during obstetric operations, but leads to an increase in the frequency of cesarean sections when predicting prolonged labor [27]. The use of ultrasound examination in childbirth does not allow to diag-
nose anomalies of labor activity (weakness, discoordination of labor activity) in the first and second periods of labor [34].
There are two main situations in which intra-natal ultrasound examination is advisable [15, 22].
The first situation is a suspicion of weakness of labor activity in the first or second period of labor, as well as the need for differential diagnosis of clinical inconsistency of the fetal head with the pelvis of the delivery woman. In this case, you should focus on the angle of progression or the distance from the fetal head to the perineum during transperineal ultrasound, as well as on the position of the fetus during transabdominal ultrasound.
The second situation is predicting the success of operative vaginal delivery (including manual rotation of the fetal head from the posterior view of the occipital insertion to the anterior one). In this case, the practitioner should evaluate the position of the fetal head during transabdominal ultrasound and the position of the head relative to the spinal plane — during transperineal ultrasound. The most reliable sonographic parameters for predicting the result of this procedure are the distance from the head to the perineum and the angle of progression; an assessment of the median angle and/or direction of the fetus may also be useful.
The use of ultrasound navigation in childbirth cannot and should not completely replace vaginal examination. If, however due to various circumstances (expressed tribal tumor, asynclitic) to obtain reliable information via this is impossible, the echographic pattern can become a reliable assistant practitioner, especially in situations when the question about the appropriateness of surgical intervention [19].
Ultrasound examinations in the postpartum period
The postpartum period is called the first 6 weeks after delivery. For the first time, ultrasound examination for the study of postpartum changes was used by H. P. Robinson in 1972 [36].
Although the postpartum period is a time of physiological involutional processes, events that accompany delivery through the natural birth canal or by c-section often lead to complications in a significant number of patients. These negative consequences are most often associated with the occurrence of bleeding or an infectious process.
When assessing postpartum bleeding, the ultrasound method is used as a source of diagnostic information, which is due to its exceptional diagnostic value, mobility and safety of modern devices [29].
During ultrasound examination, it may be difficult to make a differential diagnosis between clots, which are generally more homogeneous, and placental fragments, which are characterized by areas of increased echogenicity in their structure. B. S. Hertzberg and J. D. Bowie [17] proposed to distinguish 5 types of echographic picture of the uterine cavity in patients with suspected placental tissue remnants. According to their data, the most characteristic sign of the presence of residues was the detection of a volumetric hyperechoic formation in the uterine cavity.
Another problem of the postpartum period in modern obstetrics is infectious and inflammatory diseases, which is due to their high frequency - 5-26% and their role in the structure of maternal mortality. Subinvolution of the uterus and hematolochiometry are characterized by an increase in the quantitative indicators of three-dimensional Dopplerography in all parts of the uterine vasculature due to pronounced vascular dilatation, and subclinical and clinical forms of endometritis are characterized by a decrease in the quantitative indicators of three-dimensional Dopplerography in all parts of the uterine vasculature due to pronounced discoordi-nated vascular disorders [46].
The incidence of uterine scar failure after c-section is 10-15%, while the proportion of abdominal delivery has been steadily increasing in recent years. Thus, ruptures of the uterus along the scar after the previous c-section occur in 0.62-9.0% of cases and often cause antenatal and intranatal fetal death, and life-threatening bleeding for a pregnant woman [38].
One of the main methods of assessing the condition of the scar on the uterus during pregnancy is ultrasound. However, the information about the diagnostic value and possibilities of transvaginal and transabdominal ultrasound examination differs significantly between domestic and foreign authors, and tactical approaches remain ambiguous [11, 32, 47].
Conclusion
When I. Donald, J. MacVicar, and T. G. Brown published the first obstetric ultrasound image in the Lancet in 1958, they could not have imagined the enormous progress and extensive use that ultrasound would achieve in prenatal diagnostics over the following decades. Ultrasound examination has become an integral part of diagnostics in obstetrics and gynecology. In just a few decades, the use of ultrasound in medicine has undergone significant changes: from diagnosing the presence of life in the uterine cavity to measuring the size of the fetus, from determining the morphology of the fetus to assessing its blood flow and development dynamics.
In terms of the absolute number of ultrasound studies, they were close to X-ray studies, and at the same time, the boundaries of its use were significantly expanded. First, it was used to study those objects that were previously considered inaccessible for ultrasound evaluation (lungs, stomach, intestines, skeleton), so that now almost all organs and anatomical structures can be studied sonographically. Secondly, the practice includes intracorporeal studies carried out by introducing special micro-sensors into various cavities of the body through natural openings, by puncture into blood vessels and the heart, or through surgical wounds. This resulted in a significant increase in the accuracy of ultrasound diagnostics. Third, there are new directions of using the ultrasound method. Along with routine routine examinations, it is widely used for emergency diagnosis, monitoring, screening, and monitoring of diagnostic and therapeutic punctures.
To date, ultrasound diagnostics continues to actively develop and improve.
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