Cardiotocography is used to monitor fetal HR and maternal contractions during labour. It is important as abnormalities in fetal HR in relation to contractions can indicate various complications.
This is an example of a CTG trace.
Below is a table showing the main CTG abnormalities to know and their causes:
If you wanted to look more into how to read a CTG etc this is a good resource:
https://geekymedics.com/how-to-read-a-ctg/