Cardiotocography (CTG) is a simultaneous recording of fetal cardiac activity and uterine contractions in the dynamics, carried out using phonocardiography and Dopplerometry. A cardiotocogram consists of two graphs – a tachogram (fetal heart rate on a timeline) and a hysterogram (intensity of uterine contractions in dynamics). Based on cardiotocography data, it is possible to judge the effect of contractile activity of the uterus on uteroplacental circulation and make a decision on the most appropriate tactics of childbirth.
Cardiotocography is a standard method of monitoring the condition of a pregnant woman and fetus. Currently, obstetrics carries out this examination on a planned basis in the third trimester of pregnancy at least twice. The decision on the frequency of cardiotocography is made by an obstetrician-gynecologist who performs pregnancy management, according to the analysis of the clinical situation. In certain conditions , CTG is prescribed additionally:
- Burdened obstetric anamnesis: abortions (surgical termination of pregnancy), ectopic pregnancy, inflammatory and tumor diseases in the woman’s anamnesis, late first pregnancy.
- Complications of the current pregnancy: gestosis, lack of water, the threat of termination of pregnancy, overgrowth, suspicion of intrauterine malformations, Rh conflict.
- Somatic diseases of a pregnant woman: arterial hypertension, systemic diseases, chronic pathologies of internal organs.
- Unfavorable indications of the previous CT scan.
- Dynamic monitoring of the course of the first period of labor.
Methodology of conducting
The cardiotocograph receives signals from sensors located on the abdominal wall of a woman lying on her side (at the point of maximum listening to heart tones), and converts them into electrical impulses characterizing the change in the interval between two subsequent contractions of the fetal heart, which it then registers as a graph on a tape, where time in seconds is marked on the abscissa axis, and a minute-by-minute fluctuation of the heart rate is recorded on the ordinate axis. Synchronous removal of data on uterine contractions makes it possible to assess the effect of uterine activity on the condition of the fetus. Fetal heart rate is recorded within 40-60 minutes due to the need to evaluate the activity of the heart in the resting phases and fetal activity.
Interpretation of results
Fetal cardiac activity is characterized by several indicators, the main one among which is the basal heart rate (the average frequency recorded for 10 minutes or more). The rate of basal heart rate is 110 – 160 beats per minute. Tachycardia of more than 200 beats per minute, accompanied by pronounced rhythm disturbances, indicates pathologies of cardiac conduction, a heart rate of more than 240 beats / min indicates fetal heart failure.
Bradycardia (decrease in basal heart rate) is usually a sign of fetal hypoxia, but it can often be a response to hypothermia, taking certain medications, prolonged compression of the fetal head in the birth canal. Sometimes bradycardia persists for a long time, but the children born do not have signs of hypoxia or other pathology.
In the case of pathological changes in the fetal heart rhythm, additional studies of its reactivity are performed, analyzing changes in heart rate under the influence of various factors. To do this, a number of evaluation tests are used: non-stressful (study of reactions to natural stimuli) and stressful (reaction to specific stimuli – physical and medical stress of the mother, changes in the composition of gases in the air mixture, reflex reactions, etc.). Based on the data obtained by cardiotocography, the doctor decides on the choice of tactics for childbirth.
Fetal heart rate is not a constant value and is subject to fluctuations under the influence of a wide variety of factors: pregnancy period, uterine tone, general condition of the mother, time of day, as well as individual fetal health and development. The sex of the child and the serial number of the present pregnancy do not matter in this context. Certain pathological conditions are characterized by a specific reaction from the fetal heart in the form of an abnormal change in heart rate. Thus, CTG is one of the simplest methods of screening for abnormalities during pregnancy in the second half of pregnancy in terms of practical application, since a stable cardiotocogram at earlier stages is practically not recorded.