At what month is the 3rd ultrasound performed? Third ultrasound during pregnancy: when it is done, norms, interpretation. Baby's internal organs

An ultrasound examination can be called the “eyes” of a gynecologist, with the help of which he observes the course of pregnancy throughout its entire duration. New 3D and 4D technologies provide such clear images of the fetus that many of the smallest details of the child’s development can be seen. Ultrasound is performed several times. This is one of the safest methods of examination during pregnancy. We will consider perhaps the most important and informative - the third planned ultrasound.

Goals and timing of the study

At what week is it better to have the third ultrasound? At 30-34 weeks of pregnancy, the final formation of all organs and systems of the child occurs. He experiences the maximum need for nutrients, which are delivered through the placenta and umbilical cord. How the birth will proceed and what vital signs the child will be born with depends on the “health” during this period.

Now it becomes clear why and when the third ultrasound is performed. The main objectives of this procedure are:

• Determination of fetal position. In the second trimester of pregnancy, the baby moves freely in the uterine cavity and can change position at any time. When a woman undergoes her third ultrasound during pregnancy, the presentation of the fetus is already formed (cephalic, pelvic, transverse).
• The study makes it possible to clarify all the dimensions of the fetus: its weight, body proportions, head circumference, and the length of individual parts of the body. Not only the sizes themselves are important, but also what week of gestation they correspond to. “Large fetus” requires special attention during delivery.
• 3rd trimester screening assesses brain development. At the same time, signs of intrauterine infection become noticeable. Sometimes, after an ultrasound at 32 weeks of pregnancy, doctors decide on an emergency delivery based on vital indications for the fetus.
• Study of amniotic fluid, which indirectly indicates the normal development of the baby.
• Final confirmation of the readiness of the mother's birth canal for natural childbirth. If, as a result of the 3rd screening, space-occupying formations or incompetence of the cervix are detected, then a decision is made on a Caesarean section.
• At this time, the respiratory movements of the fetus and its motor activity are already well determined. Deviation of indicators from the norm indicates intrauterine hypoxia and the need to look for its cause.

Interpretation of the ultrasound examination allows you to set the date of birth and decide on its method (natural or surgical).

What do ultrasound indicators mean in the third trimester of pregnancy?

When a woman receives an ultrasound report of the third trimester, she has many questions: what is considered normal, where there are deviations. In order for you not to be nervous until the moment you receive a consultation with your gynecologist, we will describe some significant parameters.

Condition of the placenta

The first point determines the location of the placenta - along which wall it is attached to the uterus. Usually this is the anterior or posterior wall of the uterus with a slight transition to the sides. The distance between the lower edge of the placenta and the cervix is ​​of great importance. In the third trimester, this distance should be at least 7 cm. If the edge of the placenta extends into the cervical cavity, this is called placenta previa, which increases the risk of premature abruption. There are cases when the placenta completely covers the cervix. This is a 100% indication for Caesarean section.

The thickness of the placenta should be 26-44 mm. An increase in this indicator in any direction indicates placental insufficiency. The child does not receive enough nutrition. Various complications may occur (intrauterine hypoxia, birth trauma).

Position of the fetus in the womb

The degree of maturity corresponds to the second. If at this stage maturation to the third degree has occurred, this is premature, and the placenta may not cope with its function for several weeks before birth. Sometimes areas of calcification are described in the placenta, which is especially frightening for pregnant women. This indicator is not so important, since neighboring areas of the placenta compensate for the activity of calcified ones.

The amount of amniotic fluid is about 1700 ml. The amniotic index ranges from 77-269 mm at 32 weeks of gestation. Polyhydramnios or oligohydramnios most often indicates intrauterine infection of the fetus, complications on the part of the pregnant woman, a conflict regarding the Rh factor, or malformations of the child.

In the third trimester, the amniotic fluid is no longer completely clear. Suspensions are found there, which are pieces of fetal skin. This is the norm, not a pathology.

Fruit size

Ultrasound screening at 32-34 weeks describes in detail the fetus, which is almost fully formed. The dimensions must fit within the following parameters:

• Biparietal head size (BSD) is the distance between the parietal bones of the skull. Normally it should be 85-89 mm.
• Abdominal volume (AB) - 8-10 cm.
• Head volume - 8.7-10.4 cm.
• The fronto-occipital size of the head (LZR) is 10-11.7 cm.
• Femur length (DB) - 5.7-7.0 cm.

These are the main dimensions that are compared with tabular values ​​and the correspondence between the size of the fetus and the gestational age is calculated. A deviation of no more than 2 weeks is considered normal. Additionally, the bones of the face, the size of the lower leg and forearm are examined.

Internal organs

It is the third screening during pregnancy that gives a complete picture of the condition of all organs of the child. It is especially important to examine the brain. Reconstruction of all parts of the brain became possible after the introduction of 3D sonography.

No less important is the degree of lung maturity (normally 2-3 at this stage), which is the most important indicator of the child’s viability after birth.

They also examine whether the face, abdominal organs, and spine are normally formed. Finally, the sex of the child is finally confirmed.

Biophysical profile assessment

The size of the fetus is an important indicator, but it does not characterize how “comfortable” the baby is in the mother’s belly. The physiological health of the baby is assessed according to the following parameters:

• the number of movements (in the 30 minutes that the procedure lasts, the child must move at least 3 times);
• number of breathing movements;
• the child’s posture (bent limbs, clenched fingers) and his facial expression (with 3D ultrasound).

By changing these indicators, you can immediately understand that the child is experiencing oxygen starvation or is suffering from an intrauterine infection.

Condition of the birth canal

Before giving birth, you need to determine how prepared the woman’s body is for this important process. Screening during pregnancy at 32-34 weeks gives an idea of ​​the condition of the cervix. If it shortens, smoothes out and the external os is slightly open, then childbirth is just around the corner. Ultrasound can also determine the tone of the uterus. Its excessive increase warns of the possibility of premature birth.

Ultrasound technique

Routine ultrasound during pregnancy does not require special preparation. Unlike the first ultrasound, you do not need to follow a diet. If the period of 12-14 weeks requires filling of the bladder for better visualization, then during the third ultrasound the amniotic fluid serves as the conductor of the ultrasound wave.

The third screening is carried out only through the anterior abdominal wall. During this period, it may be difficult for a woman to lie on her back for a long time, so before the procedure it is better to place cushions under the lower back or buttocks.

A special gel is applied to the pregnant woman’s belly, and the doctor begins to conduct an examination using a sensor. The woman and the doctor can follow the picture on the monitor. This is especially “interesting” with 3D and 4D ultrasound, which make it possible to obtain a three-dimensional image of the baby.

IMPORTANT! Deviation from normal values ​​does not mean a “sentence”. Only a consultation with a gynecologist gives the final answer whether the pregnancy is progressing correctly and how your baby is feeling.

Ultrasound in the 3rd trimester is performed to assess the development of the fetus and the readiness of the mother’s reproductive organs for childbirth. The procedure is included in the mandatory plan and is no different from previous studies.

The 3rd trimester ultrasound is the last ultrasound examination for the entire period of gestation and is prescribed at 30-34 weeks of pregnancy.

During ultrasound diagnostics, doctors look at:

• location of the fetus in the uterine cavity;
• volumes of the baby’s head and abdomen;
• presentation;
• length of the femurs;
• the size and weight of the child;
• location and maturity of the placenta;
• development of the internal organs of the fetus.

In the third trimester, an ultrasound examination is an additional examination of the mother and embryo to exclude serious congenital pathologies and developmental delays. It also allows you to find out, with an accuracy of up to a week, how far along a pregnant woman is.

How to prepare for your last ultrasound

The screening procedure in the third semester does not require special preparation, however, there are several general recommendations.

To prepare for the last ultrasound you need:

• Bring wet wipes with you to wipe off excess gel from your skin;
• take a diaper with you if the examination takes place in a clinic;
• if necessary, take activated charcoal to reduce bloating;
• Do not drink too much water before the procedure - this may reduce the quality of the study.

In the video you can see how a baby’s fetus looks on an ultrasound at 32 weeks, as well as the degree of formation of its organs. The author of the video is Alena Ponomareva.

Norms of baby development and interpretation of results

The norms of baby development and interpretation of the results concern:

• weight and main dimensions of the fetus;
• umbilical cord blood flow;
• placenta;
• amount of amniotic fluid;
• heart rate frequency.

The general condition of the expectant mother’s body is assessed separately.

Fetal fetometry by week: table

Only a doctor can correctly decipher the data, but there are standard norms that are worth paying attention to.

In the table you can see the standard sizes of the baby depending on the week of pregnancy:

Umbilical cord blood flow examination

Doppler ultrasound, or ultrasound, is one of the ultrasound diagnostic methods that allows you to effectively determine the speed of blood movement through the vessels of the umbilical cord. The doctor can make a conclusion about the functioning of the cardiovascular system based on the results of an analysis of the heart, umbilical cord and uterine artery.

In the last trimester of pregnancy, this is especially necessary, since it allows you to find out how blood flows through the umbilical cord to the placenta and to the fetus.

Attention to the placenta!

The need to undergo an ultrasound in the third trimester of pregnancy is also due to the fact that it shows the condition of the placenta. The maturity of this organ determines the onset of labor: if the ultrasound protocol shows that its maturation has occurred earlier, the obstetrician makes a decision on premature birth.

During the last ultrasound, you can check the condition of the placenta in the later stages of its development:

1. Stage one. Usually lasts from 30 to 34 weeks. In the normal state, compactions appear in the body of the organ; the average wall thickness ranges from 23.5 to 41.6 mm.
2. Stage two. Fixed at 34–39 weeks. Some depressions are permissible in the structure, and calcium deposits become noticeable. The placenta wall is up to 44 mm.

The length from the outlet of the small pelvis to the lower edge of the organ is no more than 70 mm. The degree of maturity of the placenta should be 1.

The amount of water surrounding the child

During an ultrasound, the doctor checks:

1. The amount of amniotic fluid. If there are not enough of them, the baby will become dehydrated.
2. Water quality Normally, they should be transparent, and only towards the end of pregnancy can they become cloudy.

During an ultrasound scan of the third trimester, amniotic fluid normally takes up a volume of about 400 ml. Closer to week 37, their content in the uterus should be from a liter to one and a half.

Baby's heart rate

During an ultrasound, diagnosticians always listen to the baby’s heartbeat: this proves that the fetus is moving and actively moving in the womb.

Wherein:

• from the 11th week of pregnancy until the birth of the baby, its heartbeat should be from 140 to 160 beats per minute;
• An alarming symptom is a decrease in heart rate to 85–100 beats/min, or an increased value of up to 200 beats/min.
• In addition to the frequency of beats, the parameters of their rhythm and the peculiarity of the location of the heart in the chest are determined.

Condition of female reproductive organs

During the third trimester of pregnancy, ultrasound assesses the condition of the mother's uterus. Its length and tone are measured, and the general condition of the organ is determined.

An important indicator is the length of the cervix. Normally this figure is 30 mm. The external and internal os of the organ must be closed.

Photo gallery

The photo shows screening images made using ultrasound examination.

Knowing at what stage the third ultrasound is performed during pregnancy, you will be able to monitor all stages of the child’s development until his birth.

From the article you will learn everything about the features of late-term ultrasound, and will also find the standards by which doctors assess the condition of the unborn baby.

Despite the fact that this procedure is not mandatory for women in Russia, the vast majority of doctors agree that ultrasound today is the safest way to monitor the development of the fetus and the health of it and the mother at different stages.

Surely everyone knows that ultrasound is used not only during pregnancy, but also in cases where it is necessary to determine the presence of damage to internal organs.

However, in the case when the procedure is performed on a pregnant woman, a special device is used, the rays of which are several times weaker than during a simple medical examination, therefore, the possible risk will be significantly lower than with a conventional procedure.

Ultrasound can also reveal a number of features of fetal development that cannot be detected in any other way.

The most important thing is, of course, the presence of possible pathologies - to identify them, procedures are carried out at the beginning of pregnancy, so that problems can be tracked and eliminated in time.

If we talk about the procedure in the last months of pregnancy, they will show what position the fetus is in, how adequately its internal systems are working, will help establish the final date of birth, and will also make it clear whether the child or mother will need additional medical intervention during and after childbirth.

As you can see, screening - another name for ultrasound - is a necessary procedure needed at any stage of pregnancy, and if it is neglected, it can lead to very negative consequences.

If the pregnancy is progressing normally and the diagnostics show appropriate results, then more than three ultrasounds will not be required.

However, if a woman experiences bloody discharge, sharp or dull pain in the lower abdomen, weakness, increased temperature, etc., this is a reason to conduct additional screening, and it does not matter what stage of pregnancy is established and how much time has passed since the onset of symptoms.

If we weigh the pros and cons, it becomes obvious that screening is still better, since the negative consequences of ultrasound exposure have not been identified, but the consequences of avoiding this procedure can be very dire.

Features of the third ultrasound

The third planned ultrasound is the last if fetal development is within normal limits. It has very clear objectives, which differ from the first and second procedures, which examine the condition of the fetus at an earlier stage of pregnancy.

The timing of the third ultrasound is at 32–34 weeks of pregnancy. During this period, attention is paid not so much to finding possible abnormalities in the fetus (the period for determining this is earlier), but to the peculiarities of its position and other factors that will affect the process of childbirth.

First of all, doctors look at the position of the fetus, as well as its physical parameters (size, weight, etc.), and assess the condition of the placenta.

It is also very important to determine how well the circulatory system and cardiac function of the embryo are working during the last scheduled examination.

The latest screening will be able to determine whether there is a risk of developing defects of the arteries and blood vessels, the disruption of which can occur precisely in the last trimester of pregnancy.

Due to the fact that the gestational age is already quite long and the fetus is clearly visible, no special preparation is required for this ultrasound - at 32 - 34 weeks it is performed transabdominally, i.e. through the abdominal wall, and not from the inside.

Since the examination of the child’s blood vessels and arteries is very important in the third trimester, screening is usually carried out together with Doplerometry, which allows us to identify possible pathologies.

Research results

Like the previous screening, which is carried out at the beginning and middle of pregnancy, the third ultrasound also has its own standards, according to which they evaluate how correctly development is proceeding.

Physical parameters or fetometry are the first thing that is looked at when the third ultrasound is performed.

Existing standards make it possible to establish how large or, conversely, small the fetus is at the moment, whether there are any individual characteristics of the skeleton, etc.

Approximate norms for a fetus at 34 weeks of development are as follows: the biparietal size of the head should be approximately 80 mm, with a deviation of +/- 7 mm.

Bipariental size (between the temporal bones) – BPR or BRGP; Thigh length – Dlb; Chest diameter - DGrK

The fronto-occipital region can be from 105 to 110 mm, with a deviation of 9 mm upward or downward allowed.

The baby's head circumference should fit within the framework of 304 - 317 mm, the femur - 61 - 65 mm, the lower leg bones - up to 64 mm, the humerus - 56 - 59 mm, and the forearms - no more than 56 mm.

Of course, the indicated norm figures are only approximate and in each individual case the doctor decides for himself whether there are any deviations.

This is why there is an ultrasound transcript, which, taking into account the results of previous procedures, allows us to draw conclusions about the current state of the embryo.

A very important factor that also needs to be measured are the parameters of the placenta.

They are measured during every scheduled examination, and the last trimester is no exception.

In addition to the parameters that are set, it is also very important to establish the location of the placenta at a given time - this also helps with screening.

Localization of the placenta is very important, because... its incorrect position can lead to complications.

For example, if the placenta is located too close to the internal os of the uterus, there is a risk that the fetal head will not be able to secure itself in the desired position - this will lead to a breech presentation of the fetus.

At the moment, the norms for the placenta are as follows: up to 34 weeks, its size can range from 32 to 43 mm.

There are also norms for its structure: the placenta is normally always homogeneous, but if there are disturbances in its condition, this is fraught with the onset of inflammation.

There is also such a factor as the maturity of the placenta - deciphering the results will help determine it.

The maturity of the placenta depends on the time at which the ultrasound is performed - if it turns out that premature aging has begun, then measures must be taken, since this is fraught with impaired fetal development due to a lack of nutrients.

Almost all abnormalities in the placenta indicate that there is a risk of a lack of nutrients entering the child’s body, since this is precisely the function it performs.

The amniotic fluid that screening measures also has very clear standards that do not depend on the individual characteristics of the woman or fetus.

If development proceeds adequately, then they should correspond to a vertical diameter of 20 to 70 mm.

The last thing that an ultrasound scan at 34 weeks helps you find out is the biophysical activity of the fetus.

Its norms are individual, depending on the period, and do not have clear indicators: the doctor simply assesses how correct the breathing, tone, heartbeat and other indicators of the fetus’s vital activity are.

Additional Research

At 34 weeks, screening is usually done together with Doppler ultrasound - although there is no uniform standard, doctors advise women not to refuse this study, since it provides very important results that cannot be obtained in any other way.

It is carried out using a special device that allows you to measure the quality of blood flow, blood supply to the internal organs of the fetus, and also to identify the presence of disturbances in the functioning of blood vessels, which, if present, usually appear in the third trimester of pregnancy.

In addition, with the help of this study, the doctor assesses whether the child’s cardiovascular system is functioning within normal limits, how well the umbilical cord is supplied with blood, and whether there is a lack of blood in its veins and arteries.

With the help of this study, it is possible to determine whether there is a risk of developing hypoxia in the embryo, which means it is better to prepare for childbirth.

When a Doppler study is performed, the doctor also receives data on the quality of the uteroplacental blood flow.

Quite clear standards of indicators exist for these results. For example, the resistance index allows doctors to determine how well the blood supply to the fetus is currently flowing and, based on this, assess the general condition of both the unborn child and the mother.

The doctor obtains the desired result by assessing the systolic and diastolic speed of blood flow and comparing it with the maximum speed of blood flow.

The systolic phase reflects the maximum pressure and blood velocity during the period of heart contraction, while the diastolic phase shows the opposite result.

By calculating the difference between the maximum systolic and diastolic blood velocity, the doctor will be able to determine the pulsatility index of the uterine arteries, which normally should correspond to a value from 1.6 to 2.1 with an interval of 0.34 - 0.6.

Such values ​​also help determine how well the nutrients are delivered to the fetus and whether there is a risk of delaying its development.

The last value that is measured using this procedure is the ratio of the speed of blood flow, i.e. the blood supply to the umbilical cord arteries. This value should not exceed 4.7.

Not all women know about the importance of Doppler examination in the last period of pregnancy, but doctors advise not to neglect this procedure, because it makes it possible to obtain the most complete picture of the condition of the unborn baby.

Types of ultrasound

Most often, women undergo a standard ultrasound - it shows the fetus on one side, and also makes it possible to determine the sex of the child in the second and third trimester of pregnancy, although only if its position allows it.

However, standard screening today is not the only opportunity to see your future baby.

3D ultrasound has become quite widespread. It differs from the usual one in that the ultrasonic waves are not directed directly, but in different directions, due to which the image turns out to be three-dimensional.

This makes it possible to examine the fetus from different angles. In this case, it is possible to determine the sex of the child with 100% probability. There is also a more advanced technique - 4D screening.

It has the same functions and capabilities as any other study, but is able to provide a four-dimensional picture, as well as a motion image, due to which you can see how the child moves in real time.

However, even if you choose a standard ultrasound, you can be sure that with its help you will be able to cover all important aspects of embryo development.

In addition to different devices, the methods of performing ultrasound also differ. In early pregnancy, it can be performed internally.

This is due to the fact that the fetus is still too small, so scanning through the abdominal wall in most cases does not lead to the desired result and does not provide comprehensive information.

This type of ultrasound is also safe and virtually painless, but requires little preparation, unlike screening through the abdominal wall, which is carried out without any additional preparation.

Ultrasound is an essential element of pregnancy management, so when you find out about its onset, you should not neglect it.