Fetal Heart Rate Testing: Bradycardia

Introduction

• Description: Bradycardia is a decrease in the baseline heart rate, generally below 120 beats/min. Moderate bradycardia is generally defined as 80–100 beats/min, and severe bradycardia as less than 80 beats/min, for more than 3 minutes.

• Prevalence: Mild fetal bradycardia is observed during approximately 2% of labors.

• Predominant Age: Reproductive age.

• Genetics: No genetic pattern.

Etiology and Pathogenesis

• Causes: Depressed fetal oxygenation (placental dysfunction, abruption), fetal acidosis. Effects of maternal condition (hypotension, medication, position, significant hypothermia), congenital fetal heart block, paracervical block, head compression (during final descent of the fetus, especially in the occiput posterior position).

• Risk Factors: Fetal hypoxia, reduced placental perfusion (maternal or fetal side), maternal sedation, fetal occiput posterior position.

Signs and Symptoms

• Baseline heart rate below 120 beats/min (110 beats/min in some countries or studies)

Diagnostic Approach