mCTG stands for cardiotocography. During an external CTG scan, two transducers are placed on your body. These detect the baby's heartbeat and nerve activity. Monitoring sessions can go on for half an hour, and give an all-round indication of how baby is doing.
A CTG can be performed during pregnancy and during childbirth. During childbirth, heart rate and nerve activity can also be measured internally. The advantage to this is that the heart rate measurement is more accurate and the strength of the beats can be measured more precisely. An internal scan can only be done if you already have access and your waters have broken. A thread is then inserted with a small type of screw.
Possible reasons for a CTG include: