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During the second trimester of pregnancy, it is important for women to undergo a routine ultrasound examination or screening for a period from the 18th to the 21st week. The most pleasant thing about this procedure is the fact that during the ultrasound of the second trimester it becomes possible to determine the sex of the unborn child, which is not mandatory for doctors, but is always very desirable for future parents.
Second trimester ultrasound goals
When assessing the condition of the fetus and expectant mother during screening in the second trimester of pregnancy, it is important for doctors to estimate the number of developing fetuses, since multiple pregnancies may not be detected at the first screening. Further, the most important characteristic is the presentation of the child (that is, its location up or down with the head), its body weight and dimensions, which must comply with the standards established for each specific period of embryo development, the occurrence of entanglement with the umbilical cord of the fetus and the condition of the umbilical cord itself.
The heart rate is always measured, the presence and type of facial bones in the skull are specified (sometimes the occurrence of Down syndrome is confirmed or excluded), the length of paired bones is determined, the condition of the spine and chest is assessed.
It is important to measure the volume of amniotic fluid, as well as assess the condition and maturity of the placenta at the time of the study. In the unborn child, the anatomical features of all visualized internal organs, such as the brain, liver, kidneys, heart, lungs, are considered, and their pathologies are determined, if any. The mother is assessed for the presence of the tone of the walls of the uterus and the pathology of the cervix in order to determine the tendency to preterm birth.
Technique and fetometry of ultrasound examination of the second trimester
For ultrasound in the second trimester of pregnancy, the patient does not need to somehow specially prepare, since the presence of amniotic fluid replaces the need to fill the bladder, and the intestines, regardless of gas formation, are displaced in the abdominal cavity by the growing uterus.
Ultrasound of the second trimester is performed by transabdominal examination, when the study of all the parameters necessary for a specialist takes place through the anterior abdominal wall. The belly of the pregnant woman is lubricated with gel and the specialist guides the sensors of the ultrasound machine through it.
The main objectives of the study on the second ultrasound are the following indicators of the size of the unborn child (fetometry):
- Head circumference;
- biparietal head size;
- the size of the fronto-occipital zone of the head;
- abdominal circumference;
- the ratio of the circumference of the head to the circumference of the abdomen;
- head shape or cephalic index, which is equal to the ratio of the biparietal size of the head to the fronto-occipital zone;
- the ratio of the biparietal size of the head to the length of the femur of the child;
- the length of the femur, tibia, humerus, radius and ulna of paired tubular bones;
- the ratio of the length of the femur to the circumference of the abdomen.
At the same time, all changes in the size of the child’s body, seen at screening in the second trimester of pregnancy, must correspond to the growth rates, gestational age and pregnancy, which were previously established by specialists. So it becomes possible to determine the causes of developmental delays and prevent their further progression.
When detecting intrauterine pathologies in the development of a child, doctors talk about their symmetrical or asymmetric forms. With symmetric intrauterine growth retardation in the fetus, symmetry is observed in the development of all organs and systems, and their lag in terms of fetometric indicators is absolutely synchronous.
When an asymmetric intrauterine growth retardation occurs, usually the volume of the child’s abdomen does not correspond to the norm accepted for a given gestational age, the ratios of the head circumference to the abdominal circumference, as well as the length of the femur to the abdominal circumference, are exceeded. At the same time, the dimensions of the length of the femur and head remain normal.
Experts say that in practice, 3 degrees of fetal development lag behind the accepted norms are most common, when at the first stage the fetus can lag behind in development for up to 3 weeks, at the second up to four and at the third – more than 5 weeks.
Assessment of the internal organs of the child with ultrasound
The internal organs of the unborn child during the ultrasound examination in the second trimester of pregnancy are necessarily scanned in order to determine or exclude developmental anomalies. At the same time, doctors evaluate:
- transverse multi-level sections of the head;
- brain;
- facial structures;
- spine;
- chest;
- a heart;
- internal organs such as the liver, kidneys, stomach, spleen, intestines, diaphragm.
To exclude anomalies in the form of head development, specialists screen the cross section of the head at various levels. This allows you to visualize the appearance of a lemon-like and other head shapes, determines the severity of brachycephaly or dolichocephaly, reveals the occurrence of a double contour of the head (hydrocephalus), and also allows you to draw a conclusion about the integrity of the cranial bones.
When evaluating the state of the child’s brain, it can be concluded that ventriculomegaly occurs, when the size of the brain ventricles increases in size. Also on screening, cysts of the vessels of the ventricle of the brain, intracerebellar pathologies, intracranial formations and formations on the surface of the skull are visible.
With an increase in the distance between the eye sockets, an open mouth, a protruding tongue, experts talk about the possible development of Down syndrome. At the same time, other parameters of this anomaly are carefully studied, for example, shortened bones of the legs or heart defects.
At screening, diagnosticians necessarily consider the development of the upper and lower jaws and the profile of the child, his eye sockets in order to detect anophthalmia or cyclopia, the presence of a cleft between the lip and palate, which indicates a “cleft lip” or “cleft palate”, the occurrence of protrusion of the upper jaw. When diagnosing a baby’s spine, it is important to determine its splitting in combination with the occurrence of pathological conditions of the spinal cord. And the purpose of scanning the chest of the unborn child is to identify pleural or pericardial effusions, when a two-millimeter fluid level, taken as the norm, is exceeded in the pericardial cavity.
A study of the lungs of the fetus is carried out to determine the degree of their maturity. The degree of lung maturity can be of three types, when at zero degree the echogenicity of the lungs of a child is lower than the echogenicity of the liver, at the first stage these 2 indicators are in line, and at the second stage the echogenicity of the lungs exceeds this liver indicator. When examining the heart, first of all, it is important to note its four-chamber structure and assess the condition and development of the main vessels. Other internal organs are also examined to visualize their normal and full intrauterine development.
Evaluation of provisional organs during ultrasound examination
The main provisional or temporary organs in medical practice include the placenta, umbilical cord and amniotic fluid during pregnancy. The most important indicator of the correct course of pregnancy is the study in the second trimester of the localization of the placenta relative to the internal pharynx of the cervix. When the placenta is fixed in the area below 5,5 centimeters from the internal pharynx, experts speak of the occurrence of low placentation, and with partial or complete overlapping of the placenta of the internal pharynx, its presentation. With these anomalies, it will be necessary to repeat the ultrasound at 27-28 weeks of pregnancy, since during this period the placenta can migrate and rise.
It is also important to assess the thickness of the placenta in the place where the umbilical cord is attached, since a value exceeding 4,5 centimeters can tell doctors about the Rh conflict, diabetes mellitus, fetal dropsy, or intrauterine infection. Placental size less than 2 centimeters indicates fetoplacental insufficiency, which must be treated with medication, since it is a sign of premature maturation of the placenta and, as a result, can cause preterm birth.
Amniotic fluid during pregnancy of the second trimester is important to study for the absence of infection of the fetus, malformations of the child and other pathologies. Polyhydramnios or oligohydramnios can indicate various problems, so experts always calculate the amniotic fluid index, which is normally 2-8 centimeters.
The umbilical cord during ultrasound is examined in order to calculate the required number of vessels in it, which should be equal to one vein and two arteries. It is also important to identify the entanglement of the fetus with the umbilical cord, count the number of such entanglements and how tight the entanglement occurs.
Also, when diagnosing provisional organs, the condition of the uterus and its cervix is always considered. With uterine hypertonicity, when a pregnant woman complains of pain in the lower abdomen and discharge with blood impurities, doctors diagnose the threat of miscarriage at a later date. Also, the walls of the uterus must be considered in order to exclude the occurrence of tumors and their rapid development. If the uterus has previously undergone surgery, it is very important to monitor the condition of the surgical scar so that it remains consistent (that is, uniform, even, more than 3 millimeters thick). With an insolvent scar, a deep niche may appear in its area, the scar tissue may become thinner, and numerous hyperechoic inclusions may appear.
When diagnosing the cervix, the patency of the cervical canal and its length (normally not less than 35 millimeters) are necessarily considered in order to exclude the occurrence of isthmic-cervical insufficiency, which occurs when the length of the cervix decreases from 30 millimeters and below.
Ultrasound examination during the second trimester of pregnancy is a very important diagnostic procedure that can demonstrate to specialists any anomalies in the course of childbearing and fetal development. At the same time, modern medicine has the ability to deal with a wide range of such anomalies, and if they are detected in a timely manner, any pregnancy can result in the birth of a healthy child and subsequent well-being in the health of the mother.