Ultrasound signs of a normal pregnancy

Normal pregnancy

The study of normal pregnancy should be carried out in a strictly defined order with determination of the condition of the uterus and the anatomy of the fetus.

The following research order is recommended:

1. Conduct an examination of the lower abdomen and pelvic organs of the pregnant woman.
2. Examine the fruit.
3. Remove the fetal head (including the skull and brain).
4. Bring out the fetal spine.
5. Bring out the fetal chest.
6. Draw out the fetal abdomen and genitals.
7. Remove the fetal limbs.

Normal pregnancy

The first ultrasound examination (US) should include a general scan of the entire lower abdomen of the pregnant woman. The most common finding is a corpus luteum cyst, which is usually detected before 12 weeks of pregnancy and has a diameter of up to 4 cm. Very large cysts can rupture, which can cause bleeding. Torsion of the ovary can also be detected.

The uterine appendages, as well as all the contents of the small pelvis, should be carefully examined for any pathology, especially cicatricial changes, large ovarian cysts, large uterine fibroids, which can interfere with the normal development of pregnancy. If pathology is detected, it is necessary to assess the size of the pathological structures and conduct dynamic observation.

Ultrasound examination during pregnancy should include systematic establishment of anatomical relationships in the fetus.

Except in cases of anencephaly, the fetal organs cannot be accurately assessed until 17-18 weeks of pregnancy. After 30-35 weeks, assessment may be significantly more difficult.

Examine the uterus for:

1. Determining the presence of a fetus or multiple pregnancy.
2. Determination of the state of the placenta.
3. Determining the position of the fetus.
4. Determining the amount of amniotic fluid.

The most important part of prenatal ultrasound diagnostics is determining the condition of the fetal head.

Echographically, the fetal head begins to be detected from the 8th week of pregnancy, but the study of intracranial anatomy is possible only after 12 weeks.

Technology

Scan the uterus to identify the fetus and fetal head. Orient the transducer toward the fetal head and slice in the sagittal plane from the crown of the fetus to the base of the skull.

First, visualize the "midline echo," a linear structure from the forehead to the back of the fetal head. It is formed by the falx cerebri, the median groove between the two cerebral hemispheres, and the septum pellucidum. If the scan is performed just below the crown, the midline structure appears continuous and is formed by the falx cerebri. Below this, an anechoic, rectangular area is defined anterior to the midline, which is the first break in the midline echo. This is the cavity of the septum pellucidum. Immediately posterior and inferior to the septum are two relatively low-echoic areas, the thalamus. Between them are two hyperechoic, parallel lines, caused by the lateral walls of the third ventricle (they are visualized only after 13 weeks of pregnancy).

At a slightly lower level, the midline structures from the lateral ventricles disappear, but the anterior and posterior horns are still visualized.

The choroid plexuses are defined as echogenic structures filling the lateral ventricles. The anterior and posterior horns of the ventricles contain fluid but not the choroid plexuses.

When scanning 1-3 cm lower (caudal), close to the upper part of the brain, try to visualize a low-echoic heart-shaped structure with the apex directed toward the occipital region - the brainstem. Immediately anteriorly, the pulsation of the basilar artery will be determined, and further anteriorly - the pulsation of the vessels of the circle of Willis.

The cerebellum is located posterior to the brainstem, but is not always visualized. If the angle of the scanning plane is changed, the falx cerebri will still be visualized.

Immediately below, the base of the skull is defined as an X-shaped structure. The anterior branches of this section are the wings of the sphenoid bone; the posterior branches are the apices of the pyramids of the temporal bones.

The ventricles are measured above the BPD definition level. Look for a full midline structure from the falx cerebri and two straight lines close to the midline anteriorly and diverging slightly posteriorly. These are the cerebral veins, and note the lateral walls of the lateral ventricles. Echogenic structures in the ventricles correspond to the choroid plexus.

To determine the size of the ventricles, calculate the ratio of the width of the ventricles to the width of the cerebral hemispheres at their widest point. Measure the ventricle from the center of the midline structure to the lateral wall of the ventricles (cerebral veins). Measure the cerebral hemispheres from the midline structure to the inner surface of the skull. The values of this ratio vary depending on the gestational age, but are considered normal if they do not exceed 0.33. Higher values should be compared with standard values for a given gestational age. Ventriculomegaly (usually with hydrocephalus) requires further in-depth examination and dynamic observation. Monitoring of the child in the early neonatal period is also necessary.

In the anterior part of the fetal cranium, the orbits of the eyes can be visualized; the lenses will be defined as bright hyperechoic points located in the front. If the necessary section is made, the fetal face can be visualized in the sagittal or frontal planes. The movements of the mouth and tongue can be determined after 18 weeks of pregnancy.

If the fetal position allows, a sagittal section should be taken from the front to visualize the frontal bone, upper and lower jaw, and mouth.

Check that all facial structures are symmetrical and appear normal, especially looking for cleft lip and palate (this requires some skill).

Also scan the posterior skull and neck to detect the rare meningocele or occipital encephalocele. Scanning from the midline and laterally will help detect cystic hygroma. (It is much easier to scan transversely over the posteroinferior skull and neck.)

Fetal spine

The fetal spine begins to be visualized from the 12th week of pregnancy. But it can be examined in detail starting from the 15th week of pregnancy. In the second trimester of pregnancy (12-24 weeks), the vertebral bodies have three separate ossification centers: the central one forms the vertebral body, and the two posterior ones form the arches. The arches are visualized as two hyperechoic lines.

Also, transverse scanning can show three ossification centers and normal skin over the spine, longitudinal sections along the entire length of the spine are necessary to detect meningocele. Sections in the frontal plane can clearly determine the relationship of the posterior ossification centers.

Due to the presence of curves, it is difficult to obtain a complete section of the spine along its entire length after 20 weeks of pregnancy.

Fetal rib cage

Transverse sections are most useful for examining the fetal chest, but longitudinal sections are also used. The level of the section is determined by the pulsation of the fetal heart.

Heart of the fetus

The fetal heartbeat is determined starting from the 8th week of pregnancy, but the anatomy of the heart can be examined in detail starting from the 16th-17th week of pregnancy. The fetal heart is located almost perpendicular to the fetal body, as it practically lies on top of the relatively large liver. A cross-section of the chest allows you to get an image of the heart along the long axis, with all four chambers of the heart visualized. The right ventricle is located in the front, close to the anterior chest wall, the left ventricle is turned toward the spine. The normal heart rate is 120-180 per 1 min, but sometimes a decrease in heart rate is determined.

The chambers of the heart are approximately the same size. The right ventricle has a nearly round cross-section and a thick wall, while the left ventricle is more oval. The intraventricular valves should be visible, and the interventricular septum should be complete. The floating valve of the foramen ovale into the left atrium should be visible. (The fetal heart is more clearly visualized than in a newborn baby, since the fetal lungs are not filled with air and the fetal heart can be visualized in all projections.)

Fetal lungs

The lungs are visualized as two homogeneous, medium-echoic formations on either side of the heart. They are not developed until the late third trimester, and at 35-36 weeks, the echogenicity of the lungs becomes comparable to that of the liver and spleen. When this happens, they are considered mature, but the maturity of the lung tissue cannot be accurately assessed by echography.

Fetal aorta and inferior vena cava

The fetal aorta can be visualized on longitudinal sections: look for the aortic arch (with its main branches), the descending aortic arch, the abdominal aorta, and the bifurcation of the aorta into the iliac arteries. The inferior vena cava is visualized as a large vessel entering the right atrium just above the liver.

Fetal diaphragm

On longitudinal scanning, the diaphragm is seen as a relatively hypoechoic rim between the liver and lungs that moves during breathing. Both hemispheres of the diaphragm must be identified. This can be difficult because they are quite thin.

Fetal belly

Transverse sections of the abdomen are the most informative when visualizing abdominal organs.

Fetal liver

The liver fills the upper abdomen. The liver is homogeneous and has a higher echogenicity than the lungs until the last weeks of pregnancy.

Umbilical vein

The umbilical vein is seen as a small, anechoic, tubular structure running from the abdominal inlet along the midline upward through the liver parenchyma into the portal sinus. The umbilical vein joins the ductus venosus in the sinus, but the sinus itself is not always visualized because it is too small in comparison to the vein. If the fetal position allows, it is necessary to visualize the entry of the umbilical vein into the fetal abdomen.

Scan the fetal abdomen to determine the location of the umbilical cord entry into the fetus and to determine the integrity of the abdominal wall.

Fetal abdominal circumference

To calculate the circumference or cross-sectional area of the abdomen for the purpose of determining fetal weight, take measurements on the section where the internal part of the umbilical vein in the portal sinus is visualized.

Fetal spleen

It is not always possible to visualize the spleen. When the spleen is visualized, it is located posterior to the stomach, has a crescent shape, and a hypoechoic internal structure.

Gallbladder of the fetus

The gallbladder is not always visualized, but when it is visualized, it is defined as a pear-shaped structure located parallel to the umbilical vein in the right half of the abdomen. Because of their close proximity in this section, they can easily be confused. However, the umbilical vein is pulsating and has connections with other vessels. The vein should be visualized first. The gallbladder is located to the right of the midline and terminates at an angle of approximately 40° to the umbilical vein. It can be traced from the surface of the liver deep into the parenchyma.

Fetal stomach

The normal fetal stomach is a fluid-containing structure in the left upper quadrant of the abdomen. It will vary in size and shape depending on the amount of amniotic fluid ingested by the fetus: the stomach peristalses quite actively under normal conditions. If the stomach is not visualized within 30 minutes of observation in a fetus at 20 weeks of gestation or later, this may be due to poor filling of the stomach, congenital absence of the stomach or dystopia of the stomach (for example, in congenital hernia of the esophageal opening of the diaphragm), or as a result of the absence of a connection between the esophagus and the stomach (in the presence of a tracheoesophageal fistula).

Fetal intestine

Multiple fluid-filled loops of bowel may be visualized in the second and third trimesters. The colon is usually visualized just below the stomach and appears predominantly anechoic and tubular. Haustra may be identified. The colon is usually better visualized in the last weeks of pregnancy.

Fetal kidneys

The kidneys can be determined starting from 12-14 weeks of pregnancy, but are clearly visualized only from 16 weeks. In cross-sections, the kidneys are determined as rounded hypoechoic structures on both sides of the spine. Hyperechoic renal pelvises are visualized inside; the renal capsule is also hyperechoic. The renal pyramids are hypoechoic and appear large. Normally, minor dilation (less than 5 mm) of the renal pelvis can be determined. It is important to determine the size of the kidneys by comparing the circumference of the kidney section with the circumference of the abdomen.

Fetal adrenal glands

The adrenal glands become visible from 30 weeks of pregnancy as a relatively low echogenicity structure above the upper poles of the kidneys. They are oval or triangular in shape and can be half the size of a normal kidney (much larger than in newborns).

Fetal bladder

The urinary bladder looks like a small cystic structure and is recognized in the pelvis starting from 14-15 weeks of pregnancy. If the urinary bladder is not immediately visualized, repeat the examination in 10-30 minutes. It is important to know that diuresis at 22 weeks of pregnancy is only 2 ml/h, and at the end of pregnancy - already 26 ml/h.

Fetal genitals

A boy's genitals are easier to recognize than a girl's. The scrotum and penis are recognizable starting at 18 weeks of pregnancy, and a girl's external genitals starting at 22 weeks. The testicles are visualized in the scrotum only in the third trimester, although if there is a small hydrocele (this is a normal variant), they can be detected earlier.

Recognition of the sex of the fetus by ultrasound is of little importance, except in cases of sex-related hereditary pathology or multiple pregnancies, in which case it is desirable to determine the zygosity and condition of the placenta.

The patient should not be informed about the sex of the unborn child until 28 weeks of pregnancy, even if this can be done earlier.

Fetal limbs

Fetal limbs are detected starting from the 13th week of pregnancy. Each fetal limb must be visualized, and its position, length, and movements must be assessed. These studies can take quite a long time.

The ends of the fetal arms and legs are the easiest to see. The fingers are easier to visualize than the carpal bones or metatarsal bones, which ossify after birth. The fingers and toes begin to be visualized starting at 16 weeks. Detecting abnormalities in the arms and legs is quite difficult.

Long bones have high echogenicity compared to other structures. The femur is more easily visualized due to limited motion; the shoulder is more difficult to visualize. The lower extremities (fibula and tibia, radius and ulna) are the least visualized.

Fetal thigh

The simplest way to image the femur is to scan longitudinally down the spine to the sacrum: one of the femurs will be in the cut. Then tilt the transducer slightly until the entire length of the femur is cut, and measurements can be taken.

When measuring the length of bones, it is necessary to ensure that the bone is visualized completely: if the section is not obtained along the entire length, the measurement values will be reduced compared to the true ones.