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INTRODUCTION

KEY QUESTIONS

  • What are the limitations from a management perspective of the three-category system of the National Institute of Child Health and Human Development (NICHD) for classifying fetal heart rate (FHR) patterns?

  • What are the currently available alternatives for managing Category II FHR patterns, and what data establishes their effectiveness?

  • Is there any data to establish the efficacy for the various interventions used in labor in response to a Category II FHR pattern before we resort to delivery?

  • Is it likely that reduced variability and/or absent accelerations in the absence of significant FHR decelerations is associated with fetal hypoxia and/or acidosis?

CLINICAL CASE 27-1

The patient with this FHR tracing on admission is a 29-year-old Gravida 1 at 40 5/7 weeks gestation who presents to OB Triage complaining of contractions. Her prenatal course was uneventful. There is no history of membrane rupture or bleeding, and the fetus was moving earlier in the day. Her cervix is 2 cm dilated, 90% effaced and the vertex is at a ‒1 station. Her physical exam is otherwise unremarkable. What steps are next in the evaluation and management of this patient and what is this main problem with trying to understand the FHR tracing?

In a broad sense, the goal of electronic FHR monitoring is to prevent significant fetal morbidity and mortality by providing a proxy marker of fetal oxygenation and acid-base status. The efficacy of electronic FHR monitoring has been the subject of some scrutiny due to an association between the use of EFM and increased cesarean section (C-section) rates, without a demonstrable decrease in the rate of perinatal mortality, although a strong case can be made for a reduction in intrapartum fetal death.1 Nonetheless, FHR monitoring has become ubiquitously utilized in both antenatal testing and labor management settings. Here, we describe the development of EFM, the physiologic basis of its interpretation, its comparison with other modalities of assessing fetal status, and considerations for its use in labor management.

THE DEVELOPMENT OF ELECTRONIC FETAL MONITORING

Electronic FHR monitoring was developed in the hope that intrapartum identification of hypoxia and asphyxia might lead to interventions to eliminate fetal death and neurologic damage in labor. Cerebral palsy (CP), which used to be called infantile spastic palsy, had been attributed by James Little in 1862 to damage in labor.2 He reported to the Society of London on 200 cases that had one thing in common—an abnormal characteristic of labor. Many years later, investigators were able to demonstrate in animal models the effects of sublethal levels of hypoxemia, which resulted in brain lesions, and clinical effects that were characteristic of profound neurologic damage. The effects of sudden and total asphyxia, however, were more likely to affect the brain stem, resulting in seizures, ataxia, and athetosis; however, lesions were not characteristic of CP. Later, Myers3 concluded that profound total asphyxia was not the typical ...

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