Fetal Monitoring 
 
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2.3.1.1 ST Segment: Oxygen deficiency 
Oxygen deficiency is a known cause of neurological damage. Fortunately, intrapartum 
asphyxia with neurological damage or perinatal death is unusual and we have to monitor 
many healthy fetuses to find those that are suffering [7]. The ST interval reflects the 
function of the fetal heart muscle (myocardium) during stress tests. 
During labor, we can assess the condition of the fetus from the only routinely available 
fetal signal, the ECG. 
Intervention according to ST waveform analysis has been found appropriate and it 
results in a significant reduction in the number of acidotic babies. At the same time, 
unnecessary interventions are avoided. 
2.3.1.1.1 ST waveforms 
A horizontal or upward leaning, positive ST segment and a T wave height that is stable 
and does not increase define a normal ST. 
When asphyxia becomes severe and long lasting, the ST waveform returns towards 
normal, in parallel with a markedly reduced ability by the fetus to respond. This also 
means that the same type of change in the ST interval should not be expected as 
asphyxia progresses, simply because the capacity of the fetus to utilize its defenses 
diminishes. 
An increase in T wave amplitude is the classical reaction by a fetus responding to 
hypoxia. A fetus that responds with an adrenalin surge and myocardial anaerobic 
metabolism characterizes this reaction. This pattern signifies that the fetal metabolic 
defense is intact and the fetus thereby has the ability to handle hypoxia. 
A biphasic ST is defined as a downward-leaning ST segment. 
This pattern occurs in two situations. The first is when the fetal heart is exposed to 
hypoxia and has not had the opportunity to respond. The second is when the fetal heart 
has a reduced capacity to respond because it has been exposed to previous stress 
situations and resources are lacking or have already been utilized. Biphasic ST changes 
could also be noted with disturbances in heart muscle function, such as with infections 
or malformations. It appears that the premature myocardium may display more frequent 
biphasic ST events. 
Biphasic STs are divided into three categories; Grade 1 is a downward leaning ST 
segment with the entire segment above the baseline. Grade 2 means that an ST segment