Fetal Heart Rate Testing: Periodic Changes

Chapter 190 Fetal Heart Rate Testing: Periodic Changes

INTRODUCTION

Description: Periodic changes in the fetal heart rate in conjunction with uterine contractions may occur. These may indicate fetal stress when they are persistent, are progressively deeper, or become longer lasting. Recurrent decelerations are defined as occurring with ≥50% of contractions during a 20-minute period. In the United States, decelerations in the fetal heart rate are classified by their relationship to uterine activity: early, late, and variable. The shape of the deceleration is also significant in the classification. Accelerations higher than the baseline often accompany fetal movement and are reassuring.
Prevalence: Mild and transient periodic decelerations are not uncommon during the course of normal labor. Accelerations are documented in virtually all normal labors.
Predominant Age: Reproductive.
Genetics: No genetic pattern.

ETIOLOGY AND PATHOGENESIS

Causes:
• Accelerations

Physiologic response to fetal activity or external stimuli (acoustic stimulation, scalp stimulation, fetal scalp blood sampling). Compensatory accelerations also occur following variable decelerations. These changes reflect an intact neurohormonal cardiovascular control system

• Early decelerations

Physiologic response to head compression; dural stimulation mediated via the vagus nerve (“diving reflex”); these changes are not associated with hypoxia, academia, or low Apgar scores

• Variable decelerations

Compensatory response to obstruction of umbilical blood flow

• Late decelerations

Decreased fetal oxygenation with reflex bradycardia or myocardial depression; this type of deceleration suggests the greatest fetal stress despite the relatively modest change in heart rate

Risk Factors: Early: occiput posterior position, cephalopelvic disproportion. Variable: low amniotic fluid volume, cord prolapse, abnormal lie. Late: placental aging, reduced placental perfusion (maternal disease, vascular spasm, medications).

CLINICAL CHARACTERISTICS

Signs and Symptoms

• Accelerations

Abrupt increase in fetal heart rate that reaches a maximum within 30 seconds

• Early decelerations

Shallow U-shaped, with gradual onset and resolution, generally (10 to 30 bpm), that reaches a nadir at the peak of uterine activity; rarely associated with heart rates below 100 to 110 bpm

• Variable decelerations

Slowing with abrupt onset and return, frequently associated with accelerations before, after, or both; variable in depth and duration but coincide with the compression of the umbilical cord during contraction

Related posts:

  1. Anemia
  2. Toxic Shock Syndrome
  3. Uterine Anomalies: Bicornuate, Septate, and Unicornuate Uterus
  4. Cervical Cancer

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Jun 6, 2016 | Posted by in GYNECOLOGY | Comments Off on Fetal Heart Rate Testing: Periodic Changes

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