|Click here to visit OBGYN Atlas and Gallery|
This website is part of the comprehensive online
Obstetric and Gynecology Atlas and Gallery
Hundereds of carefully categorized obgyn illustrations, and real life ultrasound scan images and clips from clinical practice with desription, user comments lightbox..etc.
Sequence of events in response to fetal distress
How to use and interpret Fetal Heart Rate (Cardiotocography)
Use of Non-stress test as part of Biophysical profile
Not in common use clinically
Fetal heart rate pattern:
Electronic fetal heart "rate” monitoring is the plotting of fetal heart rate over time, (it is not an ECG, it is just the fetal heart rate). Fetal heart rate is characterized by having a basal pattern and shows changes to this basal pattern depending on fetal environment changes:
1- Basal Fetal heart rate pattern: The pattern shows a basal "rate" of fetal heart and basal satate of "varaibility".
Unlike adult heart rate, fetal heart rate (FHR) is much faster and irregular so it is constantly moving up and down an imaginary "basal heart rate”, which is normally from 120 to 160 bpm.
The oscillations up and down this imaginary line are called variability, and, there are 2 types of variability seen during the normal tracing of the fetal heart rate:
Variability reflects the interaction between 3 forces influencing fetal heart rate:
i. Sympathetic causing tachycardia (excitatory influence)
ii. Parasympathetic causing bradycardia (inhibitory influence)
iii. Pacemaker favouring a stable basal fetal heart
So what happens is that the sympathetic system will drive the fetal heart rate up till it reaches a threshold at which the parasympathetic system starts driving the rate downwards and in the middle of this up and down struggle the pace-maker is struggling to keep the fetal heart steady at what is interpreted as "basal FHR”
2- Changes to basal FHR pattern: The fetal heart rate undergoes constant and minute adjustments in response to the fetal environment and stimuli, these adjustments are seen as change of the usual pattern; the basal FHR and the 2 variability types.
Changes from the usual pattern are what we look for to predict presence or absence of fetal hypoxia.
PS: "Fetal well-being” is a term to describe a fetus with normal growth pattern + no congenital malformations diagnosed + not in state of hypoxia or acidosis, "fetal distress” refers to fetal hypoxia and acidosis.
Changes (from the usual pattern of basal FHR and Variability) can be transient or persistent.
A- Transient changes to the FHR, of 2 types:
B- Persistent changes to FHR (lasting more than 15 minutes), there are 3 types:
SO WHAT IS THE SEQUENCE OF EVENTS IN CASE OF FETAL HYPOXIA?
1- There will be no accelerations, due to mild depression of CNS with decreased fetal activity.
2- There may be tachycardia, but this is not common, tachycardia is usually due to arrhythmia, maternal fever or medications rather than hypoxia.
3- Then there will be early decelerations due to respiratory acidosis
4- With more depression of the autonomic nervous system there will be loss of variability.
5- With development of metabolic acidosis late decelerations will set in.
6- Then with further acidosis there will be myocardial depression with persistent fetal bradycardia.
7- With more depression of the myocardium there will loss of short term variabiliity together with bradycardia, in such omnious condition the late decelerations are obscured with the bradycardia (Sinusoidal rhythm)
How to use the information listed above?
May be used to reflect fetal well-being either through pregnancy or during fetal birth, however the concept is not the same:
i. Decelerations (especially late decelerations)
ii. Persistent changes in FHR patterns (Tachycardia, bradycardia and loss of variability for > 15minutes)
Interpretation and terms used to communicate results of fetal CTG trace:
View Strips of CTG:
Intrapartum CTG trace:
During pregnancy in a healthy fetus the FHR pattern will be normal, there will be fetal movements perceived by the mother and when recorded in the Non-Stress test will show response of FHR by acceleration.
Presence of 2 accelerations in 20 minute trace is called reactive Non-Stress test
In cases of fetal distress (Hypoxia) the fetus will show decreased activity and movement, and there will be no response to movement by an acceleration, there may also be loss of variability. The trace can be extended for further 20 minutes or repeated after 2 hours or the fetal activity provoked by acoustic stimulation (sound), palpation of maternal abdomen, intake of juice (glucose), depending on the clinical situation.
Non-stress test is also used as one item in the Biophysical profile.
Biophysical profile is another more accurate method to exclude fetal distress antenatally.
It is the simple recording of 5 items each scores either 2 if normal or 0 if absent or abnormal, it is recommended that the score is done after the mother drinks some juice or has a snack to avoid a sleepy fetus, also some medications may affect the result of BPP such as Magnesium administration as well as antihistaminics.
The original 5 items scored in the biophysical profile are:
Not all items of the biophysical profile are of the same importance. Indeed NST and AF volume assessment are the 2 most important items. Amniotic fluid volume reflects a rather chronic form of fetal distress while NST reflects acute distress.
In view of this information a Modified biophysical profile had been proposed, it consists of NST together with amniotic fluid index (not vertical depth of largest pocket) if score is 4 (reactive NST and AFI >5) then it is considered reassuring.
*Recommended management based on the original BPP score and items would be:
Decision of birthing should be based on the clinical criteria as a whole not just the BPP. Elderly primigravida or diabetic patient, also patient with previous bad obstetric history as well as a fetus suffering FGR are all scenarios that may change you action for the same BPP score depending on the patient's clinical situation.
The changes in fetal ECG can be "automatically" traced using a STAN monitor (ST segment analysis). The Monitor will automatically alert for:
These changes reflect hypoxic changes more accurately than FHR monitoring, STAN specifically reflects:
Interpretition with FHR + STAN