Fetal ultrasound

Ultrasonic scanning (UZS) is a highly informative, harmless method of research and allows for dynamic monitoring of the fetus. UZS is performed if there is a suspicion of multiple pregnancy, polyhydramnios, ectopic and undeveloped pregnancy, bladder skeleton, fetal development retardation syndrome and congenital malformations, as well as placental abnormalities (attachment anomalies, premature detachment and placental insufficiency). The optimal terms for the examination are I trimester, 16-20 and 28-34 weeks of pregnancy. In case of a complicated pregnancy, UZS is carried out at any time.

Observation of the development of pregnancy is possible from the earliest stages. At 3 weeks of pregnancy, a fetal egg with a diameter of 5-6 mm is visualized in the uterine cavity. At 4-5 weeks, the embryo is identified as a linear echopositive structure with a length of 6-7 mm. The head of the embryo is identified from 8-9 weeks as a separate anatomical formation of round shape and an average diameter of 10-11 mm. The growth of the embryo is uneven. The highest growth rates are observed at the end of the first trimester of pregnancy. The most accurate indicator of gestation in the first trimester is the coccyx-parietal size.

Evaluation of the embryo's vital activity in the early period is based on the registration of its cardiac activity and motor activity. The use of the M-method allows to register the embryonic cardiac activity from 4-5 weeks. The heart rate gradually increases from 150-160 / min in 5-6 weeks to 175- 185 / min at 7-8 weeks, followed by a decrease to 150 / min by 12 weeks. The motor activity is revealed from 7-8 weeks. There are 3 types of movements: limb movements, trunk and combined movements. The absence of cardiac activity and motor activity indicates the death of the embryo. Ultrasound examination in the I and II trimesters of pregnancy allows the diagnosis of undeveloped pregnancy, anembrion, various stages of spontaneous miscarriage, vesical drift, ectopic pregnancy, abnormalities of the uterus, multiple pregnancies. An undeniable advantage is ultrasound scanning in pregnant women with uterine myoma and pathological ovaries.

In the evaluation of fetal development in the second and third trimesters of pregnancy, the focus is on the following fetometric parameters: biparietal size of the head, the median diameter of the thorax and abdomen, and the length of the femur. Determination of the biparietal size of the fetal head is performed with the best visualization of the M-structure from the outer surface of the upper contour of the parietal bone to the inner surface of the lower contour. The mean diameter of the chest and abdomen is measured respectively at the level of the valvular valves of the fetal heart and at the site of the umbilical vein entry into the abdominal cavity. To determine the length of the femur, the sensor should be moved to the pelvic end of the fetus and, by changing the angle and the plane of scanning, to achieve the best image of the longitudinal section of the femur. When measuring the thigh, cursors are placed between its proximal and distal ends.

Ultrasound is one of the most accurate methods of diagnosing the fetal development retardation syndrome. Echographic diagnosis of the syndrome is based on the comparison of fetometric indicators obtained during the study, with the normative indicators for this period of pregnancy. The optimal and at the same time reliable method for determining the estimated weight of the fetus with USS is a formula based on measuring the biparietal size of the head and the circumference of the fetal abdomen.

The possibilities of modern ultrasound equipment allow to estimate with a high degree of accuracy the activity of various organs and systems of the fetus, and also antenatally diagnose the majority of congenital malformations.

[1], [2], [3], [4], [5]

Ultrasound placentography

Ultrasonic placentography helps to establish the localization of the placenta, its thickness and structure. The placenta is located mainly on the anterior or posterior surfaces of the uterine cavity with a transition to one of its lateral walls. In a smaller percentage of observations, the placenta is localized in the uterus. The localization of the placenta in different periods of pregnancy is variable. It was found that the incidence of low placentation before the 20th week of pregnancy is 11%. Subsequently, as a rule, there is a "migration" of the placenta from the lower segment to the bottom of the uterus. Therefore, it is advisable to finally judge the location of the placenta only at the end of pregnancy.

In uncomplicated pregnancy, the stage I of the placental structure is found mainly from 26 weeks of gestation, stage II - from 32 weeks, III - from 36 weeks. Occurrence of echographic signs of various stages of placental structure before the established terms is regarded as a premature "aging" of the placenta.

Determination of the biophysical profile of the fetus

On the basis of UZS data and registration of cardiac activity of the fetus, many authors use the concept of a "biophysical profile of the fetus", including the analysis of 6 parameters: the results of a non-stress test (NST) in cardiotocography and 5 indices determined with real-time scanning [fetal respiratory movements , motor activity (DA), fetal tone (T), amniotic fluid volume (OVC), maturity of placenta (FFP).

The maximum score is 12 points. High sensitivity and specificity of fetal BPD are explained by a combination of markers of acute (NST, respiratory movements, motor activity and fetal tone) and chronic (amniotic fluid volume, maturity of the placenta) disorders of the fetus. The reactive NST even without additional data indicates a favorable prognosis, while in the non-reactive NST, the evaluation of the remaining biophysical parameters of the fetus assumes leading importance.

Indications for the determination of fetal BPF is the risk of developing placental insufficiency, intrauterine growth retardation, fetal hypoxia and asphyxia of the newborn. Examination is made on pregnant women with OPG-gestosis, who suffer from a prolonged threat of abortion, with diabetes mellitus, hemolytic disease of the fetus. Evaluation of fetal BPF can be used to predict infectious complications in the premature discharge of amniotic fluid. Determination of fetal BPF to obtain objective information is possible already from the very beginning of the third trimester of pregnancy.

Doppler examination of blood flow in the mother-placenta-fetus system. In obstetric practice, the qualitative analysis of the blood flow velocity curves, whose indices do not depend on the diameter of the vessel and the magnitude of the insolation angle, was most widely used. In this case, the main value is given to the indices determining the ratio of blood flow rates to different phases of the cardiac cycle - systolic-diastolic ratio (SDO), pulsation index (PI), resistance index (IR):

DLS = MSIS / KDSC, PI = (MSSC-KDSC) / SSC, IR = (MSSC-CDCC) / MSPS,

Where MSSC is the maximum systolic blood flow velocity, KDSC is the final velocity of diastolic blood flow, CCA is the average velocity of blood flow. The increase in vascular resistance, manifested, first of all, by a decrease in the diastolic component of the blood flow, leads to an increase in the numerical values of these indices.

The use of modern ultrasound equipment with high resolution allows to estimate the blood flow in most fetal vessels (aorta, pulmonary trunk, lower and upper hollow veins, arterial duct, general, internal and external carotid arteries, anterior, middle and posterior cerebral arteries, renal arteries, hepatic and the umbilical vein, as well as the arteries of the upper limbs). The most practical is the study of blood circulation in the uterine arteries and their branches (arcuate, radial), as well as in the artery of the umbilical cord. The analysis of blood flow in the aorta of the fetus with pathologic curves of blood flow velocities (CSC) in the umbilical artery makes it possible to assess the severity of the violations of the proper fruit geodynamics.

The basis of the mechanism that ensures the constancy of uterine blood flow in the course of pregnancy progression is the reduction of the preplacental resistance to the blood flow. This is achieved by the process of trophoblast invasion, consisting of degeneration of the muscular layer, endothelial cell hypertrophy and fibrinoid necrosis of the terminal sections of the spiral arteries, which is usually fully completed by the 16-18th week of pregnancy. Preservation of high uterine artery resistance, caused by violation or absence of trophoblast invasion, is the leading morphological substrate of disorders of uteroplacental blood circulation.

Normally, KSK in the uterine arteries after 18-20 weeks of gestation is characterized by the presence of two-phase curves with a high diastolic blood flow velocity. During the second half of the uncomplicated pregnancy, the numerical values of indices reflecting the resistance of the vascular wall remain fairly stable with some decrease by the end of pregnancy. In uncomplicated pregnancy, the values of SDS in uterine arteries after 18-20 weeks do not exceed 2.4. Characteristic features of pathological KSK in the uterine arteries are a decrease in the diastolic component of the blood flow and the appearance of a dicrotic excision in the phase of early diastole. At the same time there is a significant increase in SDS, IR, and PI values.

Normally, in the second half of uncomplicated pregnancy, there is a significant decrease in the indices of vascular resistance in the artery of the umbilical cord (AP), which is expressed in a decrease in the numerical values of SDO, IR, and PI. Before 14-15 weeks of gestation, diastolic blood flow, as a rule, is not visualized (with a frequency filter of 50 Hz), and after 15-16 weeks it is constantly recorded.

Reduction of indices of vascular resistance in AP during the II and III trimesters of pregnancy indicates a decrease in the vascular resistance of the placenta, which is caused by the intensive growth of its terminal bed, caused by the development and vascularization of the terminal villus placenta. In uncomplicated pregnancy, SDS values in AP do not exceed 3.0.

The newest method, based on the Doppler effect, is color Doppler mapping (CDC). The high resolving power of the method promotes visualization and identification of the smallest vessels of the microcirculatory bed. The use of CCC provides an opportunity to study blood flow in the branches of the uterine artery (up to the spiral arteries), terminal branches of the umbilical artery, and intervorsity space, which allows studying the features of the formation and development of intraplacental hemodynamics and, thereby, in a timely manner to diagnose complications associated with the formation of placental insufficiency.

[6], [7], [8]

Normal fetal parameters with ultrasound

The spine of the fetus is visualized as separate echopositive formations corresponding to the bodies of the vertebrae. It is possible to determine all parts of the spine, including the sacrum and coccyx.

When examining the heart of the fetus, a four-chambered section is used, obtained with a strictly transverse scan of the thorax at the level of the valvular valves. At the same time, right and left ventricles, right and left atrium, interventricular and atrial septa, mitral and tricuspid valve valves and oval opening valve are visualized sufficiently clearly. It should be noted that from the end of the second trimester and throughout the third trimester of pregnancy, there is a functional predominance of right ventricular size over the left one, which is associated with the peculiarities of intrauterine blood circulation.

The registration of the respiratory movements of the fetus helps determine their maturity (the maturity of the respiratory muscles and the nervous system that regulates them). From 32-33 weeks the respiratory movements of the fetus become regular and occur with a frequency of 30-70 movements / min. Breathing movements are simultaneous movements of the thoracic and abdominal walls. With a complicated pregnancy, the number of respiratory movements increases to 100-150 / min, or decreases to 10-15 / min; while individual convulsive movements are noted, which is a sign of chronic intrauterine hypoxia.

Using echography allows you to clearly identify the stomach, kidneys, adrenals and bladder of the fetus. With a normal pregnancy, the urine output of the fetus is 20-25 ml / hour.

From 18-20 weeks of pregnancy, it is possible to determine the sex of the fetus. The reliability of the definition of the male is close to 100%, the female - up to 96-98%. Revealing the female fetus is based on the visualization of the labia in the form of two rollers in the cross section, the male one by the definition of the scrotum with the testicles and / or the penis.