Fetal Heart Rate Testing: Reduced Variability

Introduction

• Description: Reduced variability is characterized by a reduction in the normal variation in heart rate from beat to beat that may signal fetal stress.

• Prevalence: Reduced variability is a common finding when the fetal status is compromised. It also occurs when the fetus is sleeping.

• Predominant Age: Reproductive age.

• Genetics: No genetic pattern.

Etiology and Pathogenesis

• Causes: Fetal hypoxia with neurologic depression (when decelerations are absent, reduced variability is unlikely to result from hypoxia); extreme prematurity; maternal sedation; fetal sleep.

• Risk Factors: Prematurity, maternal sedation.

Signs and Symptoms

• Reduction in the variation of heart rate to below 3–5 beats/min (most commonly associated with periodic decelerations). This must be differentiated from the sinusoidal patterns of variations that have a smooth sine wave–like pattern of regular frequency and amplitude.

Diagnostic Approach