The Pathophysiology of CTGs and Types of Intrapartum Hypoxia
Sian McDonnell and Edwin Chandraharan
Affiliation: Consultant Obstetrician and Gynaecologist, St. George’s Healthcare NHS Trust, Blackshaw Road, London SW 17 0RE, UK.
Keywords: Birth asphyxia, cardiotocograph, decelerations, fetal monitoring, hypoxia, labour, physiology.
The introduction of intrapartum fetal monitoring has failed to achieve one of its major goals - to reduce
perinatal morbidity and mortality secondary to intrapartum hypoxic events. Despite this, it remains at common place in
labour wards around the world. Although there is now a much greater understanding of fetal physiology and the fetus’
normal adaptation in labour, there continues to be around 500 intrapartum stillbirths in the UK each year, many with
avoidable factors that are related to cardiotocograph (CTG) misinterpretation. This review article aims to consider the
mechanisms for the control of the fetal heart rate as well as features of a normal CTG. It also discusses the physiology
behind abnormal fetal heart rate patterns in labour and by explaining these changes in terms of physiological mechanisms,
it is hoped that readers will better understand how the fetus adapts in labour and hence guide appropriately timed
intervention rather than intervention based purely upon pattern recognition.
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