How effective are the fetal monitoring methods in labour?
Pretty effective but they are not infallible. It is, however, extremely unusual to
be unable to detect a baby in trouble. The one charge against the current monitoring
methods that will stick is the fact that, as a result of them, there is over-intervention.
How is a baby monitored in the uterus?
In the Western world, the standard is electronic fetal monitoring. It is what is
known as a "cardiotocograph" or CTG.
A CTG continually monitors the activity of the fetal heart (hence cardio-) and also
monitors the contractions (toco-).
On looking at a trace made by the machine, a trained person will be able to distinguish
a normal from an abnormal pattern.
How does CTG monitoring cause over-intervention?
A CTG is excellent in telling a normal pattern. This means, when it indicates that
things are normal, they almost certainly are.
Unfortunately, an abnormal pattern cannot be taken at face value. Its positive predictive
value is rather poor. Some experts quote a figure of 30%
This means, about 70% of the seemingly abnormal traces will be from babies that are
perfectly happy. A doctor, therefore, has a duty to analyze each apparently abnormal
pattern and take the appropriate steps.
Fetal Blood Sampling (FBS)
So what kind of intervention is available if the CTG trace raises suspicions?
The doctors need to make a critical assessment of the situation. If the pattern is
benign enough and there is no other evidence of possible fetal distress, then waiting
and watching for developments is the logical option.
If the pattern is causing sufficient concern, then there is a way of objectively
verifying the situation. This is by taking a tiny sample of blood from the fetus
and having it analyzed by a special machine to check the acid-base balance and oxygenation
of the baby's blood.
If the pattern looks alarming and if there is little doubt that the baby needs bailing
out, then it is up to the doctor to move fast and deliver the baby by the quickest
means feasible. This could be by instrumental delivery (such as forceps or ventouse)
or by caesarean section.
How is a blood sample obtained from an unborn baby?
As mentioned above, a fetal blood sample may be required to verify whether an abnormal
CTG truly reflects a fetus in trouble.
This is obtained by making a tiny scratch on the fetal scalp (or the buttock, if
the baby is breech-presenting). A sample is made up of about two small drops of blood.
Usually, two samples will be taken, to ensure a correct reading has been obtained.
The whole procedure takes 3 - 5 minutes from beginning to end, and the results are
available within two minutes of taking a sample.
It is a truly remarkable piece of technology which has saved millions of mothers
from an unnecessary caesarean section. In addition - and probably more importantly
- it has allowed timely intervention where this is required. This is because the
results do not only show where there is distress, they also show the actual degree
of distress and therefore guide the speed of intervention, if required.