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O– Overall assessment. CTG results. CTG: Fetal status index (FSI). A fetal non-stress test (FNST). Performing an FNST. Evaluation of test results.
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O– Overall assessment
Following CTG analysis, the findings can be used to categorise the CTG as: normal, suspicious or pathological. (Table 7)
Table 7
CTG results
| Reassuring | Non reassuring | Abnormal | |
| Baseline rate (bpm) | 110 – 160 | 100 – 109 161 - 180 | < 100 > 180 |
| Variability (bpm) | 5 bpm or more | < 5 for 40 mins or more but < 90 mins | < 5 for 90 mins or more |
| Accelerations | Present | None | None |
| Decelerations | None | Early Variable Single prolonged deceleration up to 3 mins | Atypical variable Late Single prolonged deceleration > 3 mins |
| Opinion | Normal CTG (All four features reassuring) | Suspicious CTG (One non-reassuring feature) | Pathological CTG (two or more non-reassuring or one or more abnormal features) |
Summary:
• CTG with all its information content, cannot be applied to predict perinatal outcomes;
• evidence of the absence of hypoxic condition of the fetus at the time of the study, do not prove that this state will not arise during childbirth;
• favorable results CTG remain valid during the week;
• when moderate hypoxia symptoms - CTG must be repeated every day;
• CTG data are used only in combination with other methods.
CTG: Fetal status index (FSI)
This is an attribute calculated automatically, which is included in the list of mandatory indices for deciphering the CTG of the fetus. There are only 4 numbers reflecting the FSI:
The norm of FSI in pregnancy is less than 1. 0, while they believe that if the PSP is:
• 0. 8-1. 0, the study should be repeated;
• 1, 05-2, 0 presenting initial violations of the fetus's condition, treatment is indicated, re-testing is needed in 5 -7 days;
• 2. 01-3. 0 - fetal condition severe, hospitalization required;
• 3. 0 or more - urgent hospitalization / delivery is needed.
A fetal non-stress test (FNST)
A fetal non-stress test is a common prenatal non-invasive monitoring of the fetal heart rate in response to fetal movement with the help of CTG. It is used to check on a baby's health. The term non-stress refers to the fact that nothing is done to place stress on the fetus during the test. This test is based on the knowledge that when the fetus has adequate oxygenation and an intact CNS, there are accelerations of FHR with movement. Typically, a nonstress test is recommended when it's believed that the fetus is at increased risk of intrauterine destress. A nonstress test may be done after 27-28 weeks of pregnancy, most often at 32 week.
Performing an FNST
Patient should lie down with 2 transducers on the abdomen (see CTG procedure): one measures fetus' heartbeat and the other measures uterine contractions. At the beginning of the test, a baseline fetal heart rate will be determined. When patient feels the fetus' movement, she should press a button on transducer. A fetal movement would be documented on a graph, and practitioner can see how the fetus's heartbeat changed while moving. The device used to monitor the fetus’ heart rate will pick up the increase in heart rate even if the baby’s movement is too subtle for patient to be aware of it. The test usually takes about 20 -30 minutes. The results are classified as either normal (reactive) or abnormal (non-reactive). The heart rate of a healthy, reactive fetus should increase when it moves. A reactive NST is also called a reassuring fetal heart rate test (Fig. 85).
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Fig. 85. Afetal non-stress test
Evaluation of test results.
Normal (reactive /reassuring) test: a fetus that is older than 32 weeks will be considered reactive if at least twice during a 20-minute window its heart rate exceeds that baseline by a minimum of 15 bpm for at least 15 seconds. A younger fetus will be considered reactive if the heart rate increases by a minimum of 10 bpm for at least 10 seconds.
Abnormal (non-reactive /non reassuring) test: no accelerations of FHR in response to fetal movement. There are several reasons why this could happen - for example, a " non-reactive" fetus can simply sleep. Therefore, as a rule, testing is conducted from 9 am to 2 pm when fetus' biophysical activity is most evident. In any case, a non-reactive test is an indication for further assessment of the fetal condition to exclude intrauterine distress and other complications. If test is non-reactive, at first woman is re-tested. If continues to remain non-reactive, will schedule an Oxytocin challenge test.
The Oxytocin Challenge Test (OCT) also known as contraction stress test (CST): monitoring of the fetal heart rate in response to exogenous Oxytocin infusion. The OCT/CST uses the same electronic monitoring systems for FHR and uterine activity as described in the preceding section on nonstress testing.
Purpose: To assess the fetal heart rate response to contractions. The results of the test may be used to aid the decision making process regarding mode and timing of delivery.
Indications: This may include, patients with high risk pregnancies (presence of disease state in mother or fetus) or previous testing that may have indicated compromised fetal status.
Contraindications
Absolute
Placenta Previa
Preterm/Prelabor Rupture of Membranes (PPROM)
Cervical cerclage
Incompetent cervix
Relative
Multiple Gestation
History of Cesarean Section
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