ABSTRACT
There are two possible responses – which of these occurs will depend on the speed of onset of hypoxia and the rate at which it develops.
As hypoxia develops, the fetal heart rate will increase in an attempt to maintain delivery of oxygen to the brain. This rate may be within the normal range (for example, a rise from 110 bpm to 150 bpm) or above the normal range, with tachycardia developing. This is the same response as would occur in an adult. If contractions are present, decelerations will probably occur in association with them. As hypoxia progressively worsens, there is likely to be a reduction and then a loss of baseline variability; when this occurs, the decelerations may become shallower. If the level of oxygen tension suddenly worsens, the second response may occur.
