Foetal cardiotocography. View of a cardiotocography (CTG) machine measuring the heartbeat of the foetus during labour (childbirth). The heartbeat (now 129) is picked up by an ultrasound scanner (not seen) strapped to the woman's abdomen and printed as this paper trace. The CTG machine also records the strength of the powerful contractions of the uterus which occur during childbirth. This is seen as the green number at upper left. The foetus' heartbeats are closely monitored during labour in order to detect problems such as foetal distress, which occurs when the baby's oxygen supply is impaired.