Ultrasound in the third trimester during pregnancy

Screening ultrasound helps to identify many pathologies. Carrying out such a study in the 3rd trimester of pregnancy allows doctors to assess the final period of intrauterine development of the baby. This article will tell you more about the third ultrasound scan for expectant mothers.

Purpose of the study

Ultrasound examination in this period of pregnancy is necessary for the functional assessment of the intrauterine development of the fetus. The last period of pregnancy is very important for the baby. It was at this time that his body prepares for an independent life outside the mother's body.

Ultrasound examination also allows you to assess intrauterine development of the fetus and features of its anatomy. The ultrasound specialist determines the length of the baby's torso, as well as its estimated weight. Also, with the help of this study, the doctor can determine the length of the main bone elements.

The placenta is a very important fetal element. It is thanks to this organ that the child receives all the necessary nutrients and oxygen. They are necessary for the baby for his active growth and development.

Placental blood flow assessment is very important, especially during this period of pregnancy. During the study, the specialist can identify the formed pathologies of the blood vessels of the placenta. Torsion or abnormal narrowing of the blood vessels is a common finding during ultrasound scans during this trimester of pregnancy.

With the help of a screening study, you can also determine position of the fetus in the uterus and identify related diseases of the internal genital organs... Ultrasound also allows you to identify defects in intrauterine development, which are formed already in the final weeks of pregnancy. The most dangerous are abnormalities in the structure of the heart.

Emerging heart defects are a serious cause for concern. In some situations, it may even be necessary to carry out surgical treatment in order to eliminate this defect. In this case, operations are carried out after the birth of the baby.

A special study is used to determine the signs of placental insufficiency. using doppler... This test reveals a pathological decrease in blood flow in the blood vessels feeding the placenta. Doppler studies can also determine the speed of pulse waves in the placental and uterine arteries.

Dates

A routine third-trimester ultrasound is usually done at 28-34 weeks of gestation. In some cases, a complex of studies can be carried out 7-14 days earlier. Usually, the timing of the screening ultrasound is set by the obstetrician-gynecologist observing the pregnant woman.

In the normal course of pregnancy, a third screening may not be required. Usually, an ultrasound scan in this period is assigned to expectant mothers who, during the first two studies, had some kind of abnormality. Also, screening must be carried out for pregnant women who, for whatever reason, missed previous studies.

Main investigated parameters

The position of the baby in the uterus is a very important indicator, which is assessed during the third screening ultrasound. The frequency of measurement error for this criterion is usually much lower than when conducting a study during 1 screening. If the pregnancy is multiple, then doctors determine the position of all babies in the mother's womb.

Presentation is a very important criterion, which is also noted during the screening ultrasound. Usually, the baby begins to actively move in the mother's tummy already in the middle of the 2nd trimester of pregnancy. This leads to the fact that the presentation, which was established during the second screening study, may change.

It is very important to determine this parameter in the third trimester of pregnancy before childbirth. He will help doctors determine the optimal tactics for childbirth.

Doctors identify several main clinical parameters that allow assessing the intrauterine development of the fetus. To do this, they necessarily evaluate biparietal baby head size... Also measured and abdominal circumference.

Normally, there is a certain relationship between these indicators. If the circumference of the baby's tummy significantly exceeds the size of the head, then this may indicate the development of a dangerous liver pathology and be a sign of the accumulation of excess fluid (ascites) in the abdominal cavity.

Also, to identify certain orthopedic pathologies, determination of the length of the femur... The shortening of the lengths of these tubular bones can also manifest itself in some genetic diseases.

If during the screening ultrasound, any deviations from the norm were detected, then in this case the specialists also calculate some special coefficients. For this, the frontal-occipital and cephalic ratios are assessed. Also defined indices of the ratio of the abdominal circumference to the head.

To assess the functioning of the brain, ultrasound doctors determine some of its structural elements. To do this, they must examine the lateral cisterns and ventricles. Additionally, the main linear dimensions of the cerebellum are measured. The visual hillocks (thalamuses), choroid plexuses, and the transparent septum are also evaluated.

During the study, the main anatomical elements of the face are determined. It should be noted that the face of the fetus is examined both in front and in profile. The nasal bone is an important bone element that is evaluated during the 2nd and 3rd trimester of pregnancy. Also, during the study, the area of the nasolabial triangle is necessarily assessed. To exclude anomalies, the eye sockets must be examined.

Experienced ultrasound specialists can also determine the thickness and bone density of the frontal bone. The upper and lower jaws are also examined.

Longitudinal section of the spine - a very important criterion assessed during the third screening. With the help of this study, it is possible to identify various anomalies in the development of the musculoskeletal system in babies. Shortening of the length of the spinous processes may be a sign of some chromosomal abnormalities.

During the examination of the chest, multiple respiratory system diseasesas well as the fetal diaphragm. During such a study, you can view all the elements of the heart. Ultrasound can detect various valvular defects. Doppler sonography is used to detect regurgitation. During the third screening ultrasound, the fetal heart rate is also assessed.

All major blood vessels must be examined. During the study, various pathologies of the aorta, pulmonary trunk and superior vena cava can be identified. A high-resolution ultrasound machine can also detect abnormal attachment of blood vessels to the placenta.

Assessment of internal organs is very important during the third screening ultrasound. During the study, the doctor assesses the structure and presence of pathologies of the liver, gall and urinary bladder, as well as the intestines of the fetus. Modern research methods also make it possible to determine the size of the kidneys in longitudinal and cross sections. Also, using ultrasound, you can identify various abnormalities of the urinary tract.

Fetal structures are very important anatomical elements that must also be evaluated. In this case, the thickness of the placenta is measured, and the index of amniotic fluid is also determined. In each trimester in a pregnant woman, during screening ultrasound, pathologies of the uterus and its appendages, as well as the ovaries, are necessarily detected. At 34 weeks of gestation, the normal values of the determined parameters are as follows:

The biparietal size is 7.5-9.1 cm.
Abdominal circumference - 8.1-10 cm.
Head circumference - 8.6-10.5 cm.
The frontal-occipital size is 10-11.7 cm.
The length of the femur is 5.7-7 cm.
Fruit weight - 2.2-2.7 kg.

With multiple pregnancies, the weight of babies is usually slightly less. If there is a tendency towards bearing a large fetus, doctors may recommend that the expectant mother conduct another study. It is usually done just before childbirth. A large fetus with a narrow mother's pelvis is a rather dangerous condition, which in some cases can lead to caesarean section.

The normal thickness of the placenta at this stage of pregnancy is 27-44 mm. Usually, by the end of the final period of intrauterine development, the “child's” place no longer changes its localization. Migration of the placenta in the third trimester of pregnancy is possible only with the development of pathologies.

The linear distance from the lower edge of the placenta to the internal os is also an important diagnostic criterion. Normally, this value should be greater than 60 mm. If, during the study, the placenta practically covers the internal pharynx, then this may indicate an increment or its low location. This pathology can be quite dangerous and contributes to complicated childbirth.

The maturity of the placenta is another important criterion that is determined during the third screening. This indicator may be different in different periods of pregnancy. The placenta "ripens" closer to childbirth. Her immaturity in the 3rd trimester of pregnancy is a pathology, which can lead to various complications.

With excessively early maturation of the placenta in the early stages of intrauterine development, various intrauterine pathologies can also form. Overriding of this organ can lead to the development of severe hypoxia in the fetus.

It is considered normal if the maturity of the placenta is zero before 30 weeks of pregnancy. The first degree of maturity is normal already at 27-34 weeks. The second degree is determined at 34-39 weeks. The third degree is normal from 39 weeks of gestation.

The amount of amniotic fluid is a very important criterion that is assessed during the third ultrasound screening. In this period of pregnancy, the rate of this indicator is 1.7 liters. Doctors talk about pathologies in such a situation if these indicators deviate from normal values.

Decoding the results

Polyhydramnios is a pathological condition that is accompanied by excess accumulation of amniotic fluid. In the case of this pathology, this indicator increases to 2 liters.

Excessive amniotic fluid volume of more than 3 liters is already accompanied by the development of adverse symptoms. Also, this condition usually leads to the formation of dangerous pathologies. These include: abnormal presentation of the fetus, loss of umbilical cord loops, birth bleeding, as well as various postpartum diseases. In this case, the probability of fetal death rises to 45%.

In a newborn baby who was born with signs of polyhydramnios, immediately after his birth, signs of atresia of the esophagus or stomach, as well as other anomalies of the gastrointestinal tract, must be excluded. However, it often happens that polyhydramnios does not lead to any pathologies in either the mother or the fetus.

Low water is a pathology that is established with a pronounced decrease in the volume of amniotic fluid. This pathological condition is often found during prolonged pregnancy, when the expectant mother carries the baby for more than 40 weeks. In such a situation, the risk of the formation of intrauterine pathologies in the fetus increases significantly.

To assess the degree of violations, a comprehensive assessment of the mother-placenta-fetus is carried out. All identified deviations are divided into several categories:

First degree disorders... They are characterized by a compensated flow. In this case, severe disorders in the fetus are not diagnosed. If during the study any insignificant deviations were revealed, then in this case pathogenetic treatment can be prescribed. The dynamics of the state of the fetus in this case is required.
Second degree disorders... Also called subcompensated state. In this case, pathologies of placental blood flow are revealed. Treatment of these disorders in such a situation is carried out in the clinic. Hospitalization of the expectant mother in a hospital, as a rule, is not required.
Third degree disorders... They are characterized by decompensated flow. They are accompanied by severe disturbances in the placental blood flow. Such pathologies are quite rare. To eliminate the adverse symptoms in this case, hospitalization is required.

In the 3rd trimester of pregnancy, the placenta should be located on the back wall. In this case, normal placental blood flow is provided. For a normal delivery, it is better that the placenta is 4 cm higher than the internal uterine pharynx. If it shifts lower, then, most likely, the expectant mother will not be able to give birth to a baby on her own without a cesarean section.

The length of the cervix is a very important criterion that is assessed during the third screening. During this period of pregnancy, the normal values of this indicator are more than 3 cm. If this criterion is less than the norm, then this is, as a rule, a manifestation of isthmic-cervical insufficiency. To eliminate this pathology, a special application of suture material is required.

The increased tone of the uterus is a very dangerous condition, which is assessed during the third screening. This pathology can lead to premature birth and also to the development of dangerous conditions that can manifest themselves during childbirth.

A decrease in fetal heart rate, detected during the third screening ultrasound scan, is a manifestation of the pathology of the cardiovascular system. In this situation, the heart rate drops below 130 beats per minute. Tachycardia is also a dangerous symptom that can be a manifestation of fetal hypoxia. In this case, it is required mandatory prescription of therapy, which is selected by the gynecologist together with the therapist.

During the third planned ultrasound scan, performance indicators are also necessarily evaluated respiratory system... A decrease in the frequency of respiratory movements of the fetus is an extremely unfavorable symptom, indicating the underdevelopment of its respiratory organs. Too fast breathing can be a manifestation of severe hypoxia. At this stage, doctors consider a respiratory rate of 40-70 movements per minute to be the norm.