A wide range of clinical techniques and investigations is available to healthcare professionals to survey the condition of a fetus in the womb. These may be deployed from early pregnancy to birth. They range from the use of traditional equipment such as a Pinard's stethoscope, which allows direct auscultation of the fetal heartbeat, to ultrasound imaging of the fetus, which gives an ever-increasing amount of morphological and functional data about the unborn child.
This article deals with those monitoring techniques that are used immediately preceding or during childbirth - known as intrapartum fetal monitoring. Current techniques rely predominantly on the use of electronic fetal monitoring through the use ofcardiotocography (CTG). This technique records changes in the fetal heart rate (FHR) (via Doppler ultrasound or direct fetal ECG measurement with a fetal scalp electrode) and their temporal relationship to myometrial activity and uterine contractions. The interpretation of the data collected depends on the relationship between the two traces. The aim is to identify babies who may be hypoxic, so additional assessments of fetal well-being may be made, or the baby delivered by caesarean section or instrumental vaginal birth.
The technique became widely used from the 1960s onwards. Prior to this there was very little that could be discerned about the state of the fetus. The new technology was widely embraced as an undoubted 'good thing' which would lead to better outcomes and reduce the incidence of conditions such as cerebral palsy, which were postulated to be largely due to episodes of intrapartum cerebral ischaemia. Unfortunately, subsequent evidence has not borne out this optimism.
It seems unlikely that more than a small minority of cases of cerebral palsy is directly attributable to avoidable intrapartum fetal hypoxia:[1][2]
• Low gestational age (24-30 weeks) plus: postnatal dexamethasone use; patent ductus arteriosus; severe hyaline membrane disease; resuscitation in the delivery room; and intraventricular haemorrhage have all been shown to be associated with higher rates of cerebral palsy. Whereas antenatal corticosteroid use in very preterm infants is associated with a lower rate.[3]
• There appears to be at best a tenuous connection between cardiotocographic findings, what they signify about the fetal condition and any improvement in outcomes as a result of intervention based upon them.[4]
• The widespread use of electronic fetal monitoring as part of the management of normal labour has been discarded, as a result of professional and public voices.[5][6]
• A Cochrane meta-analysis showed that the routine use of intrapartum CTG had a minor beneficial effect on the incidence of neonatal seizures but no difference in rates of cerebral palsy or infant mortality. However, its use increased instrumental and caesarean deliveries significantly.[7]
• Antenatal CTG: a Cochrane systematic review has found no evidence of the usefulness of CTG in antepartum fetal assessment, although computerised CTG may have advantages but further studied are needed.[8]