Antenatal foetal heart monitoring

Antenatal foetal heart rate assessment was introduced into clinical medicine before clear evidence of any benefits had been reported. Ad hoc definitions were used to define normal and abnormal recordings resulting in a high false-positive rate for foetal compromise. The understanding of the foetal states resulted in an improved physiologically based assessment of the antenatal tracings and allowed their classification as (i) reactive - 2 accelerations in 10 min within a recording period of 120 min, (ii) unreactive - no accelerations seen in 120 min of tracing and (iii) decelerative - the presence of repetitive decelerations on an otherwise unreactive trace. This classification reduces the high rate of false-positive traces associated with recording times of less than 40 min. Traces performed on pregnancies before 32 weeks predict clinical outcome, but need to be interpreted in light of the fact the many foetuses will not show a mature reactive pattern.