In the last trimester of pregnancy, the expectant mother will have a third planned examination, which will include an ultrasound screening. This procedure is important not only for the doctors to be sure that everything is in order with the child and the woman. It is also a great opportunity to look at the baby, because now he is very big and can do a lot. We will talk about what the third ultrasound examination is in this article.
Dates
Ultrasound in the third trimester is part of the third screening, which, in addition, includes fetal cardiotocography (CTG) and Doppler ultrasound (Doppler). Most pregnant women no longer need a biochemical blood test, but in some cases it is also done. If in the first and second trimester it was the test results that were of particular importance, then at the end of the gestation period, the data obtained as a result of ultrasound diagnostics come out on top.
The third planned ultrasound scan is usually tried to appoint for the period from 30 to 36 obstetric week. The best study is considered for a period of 32-34 weeks. For many, this ultrasound will not be the third, but the fifth or sixth, it all depends on how many similar examinations a woman underwent in the first two trimesters. Ultrasound is not considered mandatory, and the Ministry of Health only recommends it, but if a woman does not want to undergo an examination, then no one has the right to force her.
Purpose and indications
The third ultrasound has several important goals:
- fetal development assessment;
- assessment of the state of the placenta;
- assessment of the maternal body's readiness for the upcoming birth;
- choice of delivery tactics.
Since ultrasound in the third trimester is not mandatory, and the woman's consent is required for it, doctors are trying to explain why you should not give up ultrasound and dopplerometry during this period.
First of all, the examination is necessary for:
- expectant mothers expecting twins or triplets;
- women who have been diagnosed with pathologies or deviations from the normal course of pregnancy at an earlier date;
- pregnant women with a severe obstetric history (in the past there were miscarriages, a large number of abortions, missed pregnancies, premature births);
- pregnant women who previously had children with congenital genetic developmental abnormalities;
- women carrying a large child, as well as women whose children had previously "shown" some developmental lag from normal values on ultrasound;
- pregnant women who have previously been diagnosed with low or insufficient placentation, oligohydramnios or polyhydramnios, as well as pelvic or transverse presentation of the fetus;
- pregnant women over 35 years old.
The reason for refusing to undergo ultrasound is sometimes the woman's unwillingness to cause anxiety and harm to the baby. The ultrasound examination procedure is harmless for the child, especially since he is already big and strong.
Preparation and method of examination
Ultrasound examination in the last third of the gestation period is performed transabdominal - through the anterior abdominal wall. There is no need to fill the bladder, the baby is perfectly visualized in the grown uterus. There is also no need to take drugs to reduce gas formation.... Even if such a delicate problem torments a woman (and this is not at all uncommon in late pregnancy!), Then a swollen intestine cannot in any way affect the quality of the ultrasound scan, it does not squeeze the pelvic organs.
The procedure lasts about 5-10 minutes, it does not cause any special inconvenience and pain. It becomes very difficult for some expectant mothers at this time to be in a horizontal position on their back, since a large baby pinches the abdominal artery, presses on the spine and kidneys of the mother. The third ultrasound scan is done only in this position, so the woman will have to endure for several minutes.
What will ultrasound show?
At the third scheduled ultrasound scan, the doctor examines the placenta with special attention, because its condition depends on how comfortable the baby will be in the mother's womb in the last weeks before birth. The state of the cervical canal, cervix, umbilical cord, the amount and transparency of amniotic fluid are no less carefully studied. If a woman previously had surgery on the uterus, including a cesarean section, then the diagnostician will carefully examine the condition of the postoperative scar.
After 30 weeks on an ultrasound, you can clearly see the child himself - his arms and legs, count the fingers on them. The doctor will measure the growth of the baby, the length of his limbs, the parameters of the head, using a special computer program built into the ultrasound scanner, or using formulas, he will calculate the estimated weight of the fetus.
The position of the crumbs in the uterine cavity on the third ultrasound will determine the further tactics of pregnancy and childbirth. If the ultrasound shows that the baby is sitting or in a transverse position, then the woman may be offered a planned caesarean section, although the baby still has time to turn into the correct position.
It makes no sense to specify the sex of the baby on the third planned ultrasound, because no matter how the baby is located in the uterus, it is already big enough, he has to take "compact" poses, tucking his legs and arms. Such poses make it difficult to examine the genitals, and the likelihood of a medical error in predicting the sex of the baby increases tenfold.
But the doctor of ultrasound diagnostics will be able to well examine the internal organs of the fetus - the heart, kidneys, lungs, stomach and intestines, as well as examine the structures and contours of the lobes of the child's brain.
Interpretation of results and norms
When undergoing an ultrasound scan in an antenatal clinic, the appointment is carried out on a first-come, first-served basis, and the doctor does not have much time for stories and explanations for the expectant mother of what he will see on the monitor of the ultrasound scanner. Most likely, in the first two trimesters, the woman has already managed to get acquainted with the basic terminology of doctors, and the ultrasound examination protocol that will be given to her will not be a big mystery to her. But if what is written is not clear, and you really want to know how the baby is developing, you will have to get acquainted with the basic concepts and standards.
On the third ultrasound, as on the second, the fetometric data of the child are measured: biparietal, frontal-occipital dimensions, the circumference of the head, chest, abdomen, as well as the length of paired bones (arms, legs). The first in the protocol will be designated precisely these parameters, which characterize the growth rate of the baby and may indicate his estimated weight at the time of the study.
Biparietal dimension (BPD) in the third trimester
This size, which shows the distance between the parietal bones of the skull, is important for adjusting the date of birth, but only in combination with the rest of the dimensions, since in the final trimester of pregnancy, BPD itself is no longer used to clarify the duration of pregnancy, as it was during the second ultrasound in the middle term of bearing the baby. But the size from temple to temple can be an informative criterion for the development of a child.
Separately, this head size cannot talk about anything, since it is customary to evaluate it only in conjunction with other dimensions. This gives an idea not only of the size of the baby, but also of the proportionality of his physique.
If the value of BPD lags behind the average standards by no more than a week and a half, most likely, we are not talking about pathology. Perhaps the child has inherited the shape of a small head from one of the parents. This version is confirmed by the fact that all other sizes of the baby are normal. If BPD is more than two weeks behind the norm, the doctor may suspect intrauterine growth retardation. In a later period, this can happen due to insufficient nutrition, if the placenta ages quickly, with hypoxia, if any, with an umbilical cord entanglement. Pathologies of the brain, such as microcephaly, are not excluded.
If the bipolar disorder of the fetus significantly exceeds the upper limit of the age norm, then doctors may suspect a large fetus, this version is confirmed by the increased size of the tummy, sternum, and sometimes limbs. If one head is more than the standard, and the other parameters are normal or somewhat lagging behind it, suspicions may fall on hydrocephalus - dropsy of the brain.
Frontal-occipital size of the fetal head
This is the dimension measured perpendicular to the BPR. This segment connects the occipital and frontal bones. Together with the bipariental size, this parameter gives a more accurate idea of the shape and size of the baby's head. This is important for the diagnosis of some pathologies, including genetic ones, as well as developmental delay.
If the third screening ultrasound showed a decrease in the size of the segment from the frontal bone to the back of the baby's head by more than 2 weeks, then these indicators are compared with BPD and other parameters. Usually the LHR does not decrease by itself, but together with the bipariental size. If at the same time the rest of the measurements are normal, then we can talk about asymmetrical developmental delay, about microcephaly. A slight deviation from the norm is characteristic of girls (they are more miniature), as well as children whose parents themselves have small skulls.
An excess of LZR is significantly higher than the permissible upper limit may indicate edema, hydrocephalus, pathologies of the central nervous system.
If the other parameters of the baby are also impressive, then the doctor makes a conclusion - a large fetus, in this case the woman may be advised to give birth by caesarean section.
Head diameter and abdominal circumference
The values shown in the table are average, guideline values. Individual fluctuations in these numbers can differ significantly from the average rate. Therefore, the timing of pregnancy for these indicators is never verified. The tummy and chest of a little man are measured solely in order to see the proportions of the body, to detect possible lag in the development of the baby.
Any ultrasound doctor knows that in the third trimester, babies grow especially unevenly, and therefore one baby is not at all like another, and comparing them with each other or with tables is a thankless task. Therefore, no one will pay special attention to small deviations, no one will frighten the pregnant woman.
However, significant deviations in the diameter of the chest and the circumference of the tummy downward can cause such an unpleasant diagnosis as IUGR - intrauterine growth retardation, entanglement with the umbilical cord. Modern medicine has enough methods to take urgent measures and support the baby with medication, if it is too early for him to be born.
In twin pregnancies, the size lag from the norm in one of the fetuses is not regarded as a developmental delay, it is considered a normal variant for multiple pregnancies.
Sizes of paired bones on the third ultrasound
During the third ultrasound, the doctor examines the various bone structures of the baby - facial bones, bones of the skull, phalanges of fingers on small hands. But measurements under the protocol are made only in relation to paired bones - femur, lower leg, humerus and forearm bones.
If, during the shortening of some bones, for example, the bones of the lower leg, previously no markers of fetal chromosomal abnormalities were detected at screenings, then a slight lag behind these average values should not cause any concern. Longer bones are not a cause for alarm, most likely, the baby will be large, and he inherited long arms and legs from dad or grandfather.
Internal organs of the baby
During the third ultrasound examination, the doctor examines the lobes of the baby's brain, measures the cerebellum. In addition, he examines important internal organs. The heart should have a four-chambered section, both kidneys should have the same size, smooth and clear contours, the degree of lung maturity is determined by the period, the closer to childbirth, the higher it is. At 30 weeks - she is the first, less often - the second.
An ultrasound scanner examines the baby's stomach, spine, gallbladder, bladder and intestines. If the doctor does not see the vices, then in the conclusion he will write - "normal" or "no peculiarities."
Fruit weight
In the third trimester, the baby is actively gaining weight. He increases it every day. And therefore, only the approximate weight of the fetus is calculated on ultrasound using the programs built into the scanner. In practice, the estimated weight is often strikingly different from the real weight (step - plus or minus 500-700 g).
These data are very conditional, because the weight of some children at 38 weeks exceeds 4 kilograms, and for some it does not reach 3 kilograms. More precisely, oddly enough, the weight of the unborn child is "predicted" by experienced midwives, who measure the pregnant woman with a measuring tape at each scheduled appointment in the consultation. Them assumptions very often turn out to be true.
Placenta, water, umbilical cord
"Child's place" or in the language of doctors - the placenta - by the time of the third ultrasound may have a single degree of maturity. Until the 30th week - it is zero. If the doctor indicates the first degree, there is nothing pathological in this - nature intended that the organ is temporary, and it gradually "grows old" closer to childbirth, since with the birth of a child, there will be no more need for a placenta.
If the maturity of the placenta at 32-34 weeks is the second or third, this may indicate that the "child's place" is aging prematurely, which means that the baby does not receive nutrients and vitamins from the mother's body, because the aging placenta copes with its responsibilities much worse ...
In this case, supportive treatment is prescribed, but if severe placental insufficiency develops, a decision may be made about premature delivery.
On the third planned ultrasound, the position of the placenta is also assessed. If it is too low to the exit from the uterus - the internal pharynx - or overlaps it partially or completely, the conclusion will indicate - "low placentation" or "placenta previa". Both of these conditions require hospitalization and hospital stay until delivery.
Doctors will observe the "child's place", if it does not rise before 36-37 weeks, then the woman will be shown a caesarean section at 38-39 weeks.
The amount of water surrounding the child is also of great diagnostic value. A decrease in this amount or an increase in it may negatively affect the condition of the child. in the womb and complicate the process of childbirth, which is just around the corner. The longer the period, the lower the amniotic fluid index, because the size of the fetus is already so large that they occupy almost all the space, there is less space for water.
The umbilical cord normally contains three vessels.
Doppler
It is the third ultrasound scan that can be performed with an extended study, which is abbreviated as USDG, and the people simply call it - Doppler ultrasound. With the help of a special program on the machine-scanner with a sensor the speed and volume of blood flow in the uterine vessels and placenta is measured... This gives an idea of how well the baby is "feeding", whether he is experiencing a state of lack of oxygen.
This study is mandatory for all pregnant women, whose babies are lagging behind in size from the average standard, for those who have reason to fear the development of Rh-conflict, as well as for women with multiple pregnancies. However, recently, Doppler ultrasound is done to all women during the third routine examination.
To describe the blood flow velocity, a special indicator is used - the vascular resistance index. Normally, from 30 to 34 weeks of pregnancy, this index is in the range of 0.34-0.61. From 35 weeks until the very birth, this value changes downward and is in the range of 0.33-0.57.
Blood flow in the umbilical cord is of particular importance to the diagnostician. Based on this value, a conclusion is made about the possible fetal hypoxia, which may even become the basis for a woman's premature delivery in order to save the child's life... Normal values of blood flow in the umbilical cord can range from 0.54 to 0.77 at 30 weeks of gestation, at 31-32 weeks, the range of values acceptable for the normal development of a child is 0.52-0.76.
At 33-34 weeks of pregnancy, a sensor that measures the rate of blood flow through the umbilical cord to the fetus shows a number in the range from 0.49 to 0.73. At 35-36 weeks, this value is in the range of 0.47-0.71. At 37-38 weeks, the vascular resistance index is 0.44-0.69.
If the index increases, blood flow decreases. This is very dangerous for children. Ideally, such a study should be carried out several times during pregnancy, starting at 28 weeks, especially if there is an indication for this. With the help of Doppler ultrasound, you can detect pathologies at their very initial stage, and provide the pregnant woman with the necessary medical care in a timely manner.
