Prediction and diagnosis of fetal asphyxia

The diagnosis of fetal asphyxia requires a blood gas and acid-base assessment. A reliable method to provide a continuous recording of fetal acid-base status in the clinical setting is not yet available. At the present time a diagnosis can be confirmed by means of periodic fetal blood sampling during labour or at delivery for a blood gas and acid-base assessment. Thus, the requirements are criteria to identify the fetus at risk for fetal asphyxia to justify the intervention for fetal blood sampling particularly during labour for a fetal blood gas and acid-base assessment.

The clinical paradigm that has been widely used to identify the fetus at risk of asphyxia combines clinical risk scoring with fetal heart rate surveillance. This has not resolved the problem due to shortfalls of each element of the paradigm that have become evident with increasing clinical experience.

CLINICAL RISK SCORING

The limitations of clinical risk scoring have been demonstrated in several studies. In our experience, 23-40% of fetal asphyxia occurred in pregnancies with no clinical risk factors [11,12]. The term 'low risk' based on clinical markers cannot be applied in regard to fetal asphyxia during labour.

In those cases in which clinical risk factors were present, a wide range of clinical complications determined risk with no single risk factor demonstrating a strong association with intrapartum fetal asphyxia. The positive predictivevaluefor both antepartum and intrapartum risk factors for intrapartum fetal asphyxia was 3%. Thus clinical risk scoring has a major problem with false positive prediction of intrapartum fetal asphyxia. Electronic fetal heart rate monitoring

The publication by Edward Hon in 1958 [13] reflects the beginning of the expectation that electronic fetal heart rate monitoring (EFM) would be useful in the prediction of intrapartum fetal asphyxia.

Observations during the 1960s and 1970s supported the contention that EFM could be a useful screening test for the prediction of intrapartum fetal asphyxia. Our clinical experience paralleled that of other investigators in this field with anecdotal examples of an association between abnormal fetal heart rate patterns and fetal asphyxia with a range of outcomes. Laboratory studies demonstrated a relationship between fetal heart rate behaviour and fetal hypoxemia and metabolic acidosis. Late decelerations have been shown to occur when fetal oxygen tension decreases below a critical level. The interval between the onset of the contraction and the onset of the deceleration reflects the time necessary for fetal oxygen tension to fall below this threshold [14,15]. Late decelerations due to fetal hypoxemia in a previously normoxic fetus are due to chemoreceptor initiated reflex bradycardia which can be blocked by atropine, while in previously hypoxic fetuses the bradycardia is presumably due to a direct effect upon the myocardium [16]. Based on such reports the use of EFM expanded rapidly in the 1970s.

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Getting Back Into Shape After The Pregnancy

Getting Back Into Shape After The Pregnancy

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