CTGs in the exam part 2: Everything you wanted to know about CTGs but were too afraid to ask.

​The above CTG shows late decelerations, suggestive of foetal hypoxia (in this case a cord prolapse), and indicates a need for immediate delivery of the baby.
Below is a crash course on cardiotocography (yes, that’s what it stands for). If you want a more in-depth (but still user friendly) review, check out Geeky Medics.com. Here’s the big headlines.
1.The CTG measures 2 things:
a.Foetal heart rate (above)
b.Uterine tone (below).
c.Each big square usually represents one minute.
2.The foetal heart rate will exhibit some variability around the normal FHR of 110-160/min. Normal variability is between 5 and 25 beats per minute.
3.A foetal heart rate of <100 is defined as bradycardia and is cause for concern.
4.Accelerations of heart rate in line with uterine contractions occur in a healthy foetus.
5.Early decelerations of heart rate (basically during uterine contraction) are also more likely than not to be physiologic.
a.Note that there is some subtlety to this, meaning it’s probably not an ACEM fellowship exam topic.
6.Late decelerations begin (as above) with the apex of uterine contraction. They occur, because at maximum uterine pressure perfusion insufficiency is maximal. In other words, late decelerations indicate foetal hypoxia, and are an obstetric emergency.
7.If you ever see a sinusoidal CTG (as in a proper sine wave) it is a critical emergency and indicates severe foetal hypoxia, anaemia or foeto-maternal haemorrhage.
 
That’s an absolutely “brass tracks” interpretation of a CTG. There is FAR more too it than that in real like (which is why it’s done by obstetricians rather than emergency physicians…)
However, if what is above is what you take into the exam about CTGs, it’s probably enough to pass the question. We are big believers in investing time in high yield topics, rather than very unlikely ones. CTG is an unlikely one, and if you read and remember this, you probably need to read no further.
We plan to make a bit of a FPFF series on “stuff you’ll never see, but just in case…”. If there’s other topics  our readership wants us to take on, let us know by our facebook page.