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Functional tests for the evaluation of the fetus
Last reviewed: 19.10.2021
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The most common in obstetric practice is non-stress and oxytocin tests.
The oxytocin test is simple, harmless and to a certain extent physiological, that is, it is a test that mimics normal births.
There are two basic conditions for carrying out the oxytocin test (RT):
- oxytocin is administered intravenously with a progressive increase in the dose from 1 to 4 mE / min;
- The test stops when late decelerations appear.
All other parameters can vary - the duration of the test, the number, frequency and intensity of uterine contractions, the technique of recording. During the test, the pregnant woman or the woman in childbirth is laid on her side in order to avoid the Poseiro effect. The most important for the clinician is a positive oxytocin test with the advent of late deceleration.
Some authors use a maternal stress test with physical work and, accordingly, a decrease in uterine blood flow, as well as a step test.
Also of interest is a test with a low O 2 content in the mixture, which is given to inhale the mother, causing hypoxia. This test is good for controlling the placental function.
The atropine test is based on the fact that atropine, passing to the fetus through the placenta, leads to a tachycardia of 20-35 beats / min, which occurs 10 minutes after the injection of atropine at a dose of 1.5-2 mg in 5 ml of a 40% solution of glucose and lasts 40-70 minutes.
Nonstress test (NST) is currently the most common and most valuable method for assessing the condition of the fetus. The duration of the test should be at least 30 minutes. However, some authors, on the basis of the conclusion that the fetus should remain at rest 50-75 minutes, suggested that a non-stress test required 120 minutes.
The use of a non-stress test in low-risk pregnancy showed that the frequency of fetal hypoxia in groups with an arecative type of heart rate curve (no slowing down or accelerating the rhythm during the observation period) or with a slowing of the rhythm was 33%, whereas in other types of fetal heart rate curves (reactive, hyporeactive and reactive group with the presence of slowing of the rhythm), the hypoxia frequency ranged from 0 to 7.7%. The test is considered reactive when there are 5 accelerations in response to fetal movements during any 20-minute time interval. A reactive, non-stressful test gives a favorable prognosis in pregnancy at 98.5%, and an unactive stress test gives an unfavorable prognosis in 85.7% of pregnant women. However, it is important to emphasize that a non-stress test is the indicator, based on the results of which it is possible to judge the state of the fetus only at the time of the test. For a long-term prediction, a non-stress test can not be used.
Most researchers believe that the number of cardiac palpitations in the norm should normally be more than 3 for 30 minutes of registration, each period of acceul- sations should be more than 30 seconds, and their number should be more than 17 beats per minute. The data for the reactive non-stress test and oxytocin test coincide completely and therefore the oxytocin test is unnecessary in a reactive non-stress test. To assess the risk of intrauterine fetal death, both tests are often of little informative.
False negative results with a non-stress test are most often observed with placental abruption, congenital developmental abnormalities and umbilical pathology.
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