Absolutely every woman during pregnancy is worried about how her baby is developing, is everything all right with him. Today, there are methods that allow a fairly reliable assessment of the condition of the fetus. One of these methods is cardiotocography (CTG), which reveals the relationship between fetal movements and heart rate. From this article you will learn what CTG is, by what characteristics it is evaluated, what indicators for fetal CTG are normal, and what affects the results of the study.
What is CTG
Cardiotocography is based on recording the fetal heart rate and its changes depending on the influence of external stimuli or fetal activity.
Diagnostics is carried out using two ultrasound sensors, one of which is strengthened on the abdomen of a pregnant woman, after determining the area of good audibility of the child’s heartbeat.
It is intended for registration of cardiac activity of the fetus. The sensor receives an ultrasonic signal reflected from the child’s heart, which is then converted by the electronic system into an instantaneous heart rate. The second sensor is fixed on the abdomen in the uterine fundus. It records uterine contractions. To improve the transmission of ultrasonic waves, the sensors are treated with a special gel. Also, modern devices are equipped with a remote control, by clicking on the button of which, a pregnant woman can observe fetal movements.
The results are displayed by the device on a paper tape in the form of a graph. It also shows contractions of the uterus and fetal movements. According to the data obtained, it is possible to judge, first of all, about the state of the baby’s nervous system, about its protective and adaptive reactions. If the CTG indicators of the fetus are the norm, then the baby feels comfortable, and his development is proceeding according to the deadlines.
What is CTG necessary for?
Examination of a pregnant woman in the office of an obstetrician-gynecologist includes listening to the baby's heartbeat with a stethoscope. Deviation from the norm of heart rate (HR) up or down indicates that the child is uncomfortable. In this case, the doctor sends the expectant mother to a more thorough study of the work of the cardiovascular system of the fetus - CTG.
There is a clear correlation between the well-being of a pregnant woman and the condition of the fetus. So, if the pregnancy proceeded calmly, without intrauterine infection, the threat of termination, gestosis, then the results of CTG are most likely to be normal. If, with the well-being of the pregnant woman, suspicious CTG results are observed, then it is necessary to re-examine the patient after a week.
If a pregnant woman has found serious changes in her health, it is necessary to conduct CTG as often as possible in order to prevent the occurrence of pathologies in the development of the fetus in time and take the necessary measures.
Features of the study
CTG is usually prescribed after 32 weeks of pregnancy, since only by this time the maturation of neuromuscular impulses occurs, and the method becomes the most informative.
For example, for CTG of the fetus, the norm is 33 weeks - the presence on the graph of more than two accelerations. By this time, they are caused by the response of the nervous system to fetal movements or to external factors. At earlier stages, the acceleration may be associated with the conditions of the fetal existence, therefore, the study may lead to false results.
Also, by this time, the fetus establishes a cycle of activity and rest, which is of great importance for this study. When performing CTG during the resting period of the fetus, the results will always be positive, even if in fact there is a high degree of hypoxia. That is why the study should be conducted for at least 40 minutes. During this time, the fetus will necessarily increase motor activity, which will allow you to register a change in heart rate during its movement.
It is very important that the woman feels calm and comfortable during the study. An uncomfortable position or vivid emotions can cause a more active movement of the fetus, which will lead to false results. Usually, during the procedure, a woman sits in a comfortable chair or lies on a couch on her side.
In order to understand how to decipher the CTG of the fetus, we will analyze in detail what parameters are used to evaluate it.
Basal Heart Rate
Basal heart rate is the average fetal heart rate calculated over 10–20 minutes. It is determined in the absence of fetal movement between uterine contractions without external stimuli, without taking into account acceleration and deceleration.
When conducting CTG of the fetus, the rate of BSHSS is 110-160 beats per minute. Tachycardia, that is, an excess of the norm of the basal heart rate, can be observed with
fetal hypoxia, anemia, malformations and insufficiency of the fetal heart function, as well as with the fever of the pregnant woman, her intrauterine infection, and increased thyroid function. Taking drugs that have a pacemaking effect can lead to an increase in the fetal heart rate.
Lowering the basal level below normal (bradycardia) may be due to hypoxia, fetal heart defects, as well as decreased maternal blood pressure, hypoxemia, prolonged compression of the umbilical cord, the presence of a cytomegalovirus infection in a pregnant woman.
Heart rate variability
This parameter is characterized by the presence of instantaneous oscillations - deviations of heart rate from the basal level. When analyzing CTG, the amplitude of instantaneous oscillations is usually studied, the nature of which emit low oscillations (deviation is less than three beats / min), medium (3-6 beats / min), high (amplitude more than 6 beats / min).
For CTG of the fetus, the norm is 36 weeks - high oscillations indicating a good state of the fetus. The presence of low oscillations indicates pathologies in its development.
Particular attention in the analysis of cardiotocograms is given to slow oscillations. Depending on their amplitude, a monotonic type is distinguished, which is characterized by a low amplitude of oscillations (from 0 to 5 beats / min), a transitional type with an amplitude of 6 to 10 beats / min, a wave-like (from 11 to 25 beats / min) and a jumping type (amplitude above 25 bpm). An increase in the amplitude of oscillations can be associated with moderate hypoxia of the fetus, as well as with the influence of external stimuli that stimulate its nervous system. A decrease in the amplitude of oscillations can be caused by severe hypoxia, which leads to inhibition of the function of the nervous system of the fetus, the use of drugs, tranquilizers.
Acceleration
Acceleration is a temporary increase in heart rate of at least 15 beats / min compared with the basal level and lasting more than 15 seconds. On a cardiotocogram, they look like tall cloves. Accelerations are a response to external stimuli, uterine contractions, and baby movements. Their presence on CTG of the fetus is the norm.
Deletion
Deceleration is the reduction in fetal heart rate by at least 15 beats / min for more than 15 seconds. The graph presents as significant depressions. Distinguish between early, late and variable decelerations. In addition, they are classified by amplitude as light with a decreased heart rate of up to 30 beats / min, moderate - 30 - 45 beats / min, and heavy - from 45 beats / min. Heart rate reduction may occur due to impaired placental blood flow, myocardial hypoxia, compression of the umbilical cord.
CTG of the fetus. Norm indicators
To assess the condition of the fetus, the World Health Organization has developed recommendations that indicate the minimum and maximum acceptable values for each of the parameters. According to these recommendations, fetal CTG (normal for 33 weeks) should have the following meanings:
- Basal heart rate: 110–160 beats / min.
- Heart rate variability within 5–25 beats / min.
- Two or more accelerations in 10 minutes.
- Lack of deep decelerations.
It is worth noting that for CTG of the fetus, the norm of 35 weeks or more is the same as in 33 weeks.
Assessment of the condition of the fetus by points
Decipher the results of CTG on a 10-point system, evaluating each criterion from 0 to 2 points. For fetal CTG, the norm of 36 weeks, as during the entire third trimester, is 9-10 points, if the total number of points is from 6 to 8, this indicates oxygen starvation (hypoxia) without urgent threats, it is necessary to repeat the CTG procedure in a week;
if 5 points or less - it means that the child experiences severe oxygen starvation, which can lead to serious neurological problems, urgent action is necessary.
It must be remembered that even if the CTG of the fetus is 8 points or slightly lower, you do not need to be scared ahead of time. In this type of study, as well as in many others, there are factors that affect the information content of the testimony. The results are highly dependent, for example, on whether the baby is sleeping or awake. Experienced doctors, when decoding cardiotocograms, take into account factors such as weather conditions, the mood of the pregnant woman, and the level of glucose in the woman’s blood. If the CTG data are not normal, then the doctor will prescribe an additional examination. Typically, cardiotocography is performed twice in the third trimester of pregnancy, but in some cases more, for example, with multiple pregnancy, high blood pressure, the presence of infections, diabetes mellitus, unsatisfactory results of ultrasound examination, bleeding, premature contractions.
Possible errors in the interpretation of CTG data
- The baby in the womb is in constant motion. Sometimes he can press the umbilical cord with his head, because of which blood flow in the vessels of the umbilical cord is disturbed for a short time, which affects the results of CTG. In this case, the cardiotocogram will have a pathological character with a good condition of the fetus.
- Sometimes during oxygen starvation , the fetus triggers protective reactions: there is a decrease in oxygen consumption by tissues and an increase in resistance to hypoxia. In such cases, the child suffers, but this does not affect CTG.
- With the development of pathology, the ability of tissues to absorb oxygen with its normal content in the blood may decrease, because of which the fetus does not react, and CTG will be normal, although it suffers due to a lack of oxygen.
Given all of the above, it should be understood that CTG of the fetus during pregnancy is a very important diagnostic method, but to obtain a complete picture of what is happening, CTG data must be compared with data from other studies. Today, ultrasound diagnostics and Dopplerometry are widely used.
Where can I do CTG of the fetus
CTGs are done free of charge in all antenatal clinics. You can conduct research in private medical centers, but for a fee.
Maternity hospitals also conduct cardiotocography during childbirth. This helps to assess the well-being of the child in childbirth and uterine contractions, to check the effectiveness of the treatment and the tactics of childbirth.
Some expectant mothers are afraid to conduct various kinds of studies during pregnancy, believing that they can harm the health of the unborn baby. Cardiotocography is absolutely safe, and you can do it as many times as necessary, without risk to health. In addition, it is painless, does not cause any discomfort.
We wish you an easy pregnancy and good health!