Fetal Heart Rate Testing: Reduced Variability

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Chapter 191 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.
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.

CLINICAL CHARACTERISTICS

Signs and Symptoms

• Reduction in the variation of heart rate to below 3 to 5 beats per minute (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

Differential Diagnosis

• Uterine hypertonus or tachysystole
• Conduction anesthesia
• Maternal hypotension
• Placental abruption
• Medication effects (magnesium sulfate, sedatives)

Associated Conditions: Prematurity, fetal stress.

Workup and Evaluation

Laboratory: No evaluation indicated
Imaging: Ultrasonography may be used to assess possible causes.
Special Tests: Fetal scalp pH (when available) may be of assistance in determining the fetal status.
Diagnostic Procedures: Clinical evaluation of mother and fetus.

Pathologic Findings

None.

MANAGEMENT AND THERAPY

Nonpharmacologic

General Measures: Maternal hydration, change in maternal position (lateral recumbent), maternal oxygen therapy.
Specific Measures: Aggressive fetal and maternal evaluation, amnioinfusion, tocolytics (when hypertonus is involved), expedited delivery in the face of nonreassuring changes.
Patient Education: American College of Obstetricians and Gynecologists Patient Education Booklet AP015 (Fetal Heart Rate Monitoring During Labor), AP098 (Special Tests for Monitoring Fetal Health).

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Drug(s) of Choice

(Tocolytics may be used if uterine tetany or tachysystole are thought to play a role in fetal stress.)
Contraindications: Tocolytics are relatively contraindicated in the absence of a diagnosis.

FOLLOW-UP

Patient Monitoring: Continued maternal and fetal assessment.
Prevention/Avoidance: Adequate maternal hydration, left lateral recumbent position for labor.
Possible Complications: Progressive deterioration of fetal status unless underlying processes are identified and corrected.
Expected Outcome: With aggressive diagnosis and management, outcome will generally be good.

MISCELLANEOUS

Other Notes: When the fetal heart rate is increased, there is an apparent reduction in beat-to-beat variability based solely on physiologic constraints and does not reflect fetal stress.
Intrapartum fetal heart rate monitoring is only one part of the overall evaluation of mother and fetus. This modality must be used to augment clinical judgment, not replace it.

REFERENCES

Level I

Ellison PH, Foster M, Sheridan-Pereira M, MacDonald D. Electronic fetal heart monitoring, auscultation, and neonatal outcome. Am J Obstet Gynecol. 1991;164:1281.

Hallak M, Martinez-Poyer J, Kruger ML, et al. The effect of magnesium sulfate on fetal heart rate parameters: a randomized, placebo-controlled trial. Am J Obstet Gynecol. 1999;181:1122.

Level II

Davidson SR, Rankin JHG, Martin CBJr, Reid DL. Fetal heart rate variability and behavioral state: analysis by poser spectrum. Am J Obstet Gynecol. 1992;167:717.

Graham EM, Petersen SM, Christo DK, Fox HE. Intrapartum electronic fetal heart rate monitoring and the prevention of perinatal brain injury. Obstet Gynecol. 2006;108:656.

Siira SM, Ojala TH, Vahlberg TJ, et al. Marked fetal acidosis and specific changes in power spectrum analysis of fetal heart rate variability recorded during the last hour of labour. BJOG. 2005;112:418.

Viscomi CM, Hood DD, Melone PJ, Eisenach JC. Fetal heart rate variability after epidural fentanyl during labor. Anesth Analg. 1990;71:679.

Level III

American College of Obstetricians and Gynecologists. Antepartum fetal surveillance. ACOG Practice Bulletin 9. Washington, DC: ACOG, 1999.

American College of Obstetricians and Gynecologists. Intrapartum fetal heart rate monitoring. ACOG Practice Bulletin 70. Obstet Gynecol. 2005;106:1453.

Burrus DR, O’Shea TMJr, Veille JC, Mueller-Heubach E. The predictive value of intrapartum fetal heart rate abnormalities in the extremely premature infant. Am J Obstet Gynecol. 1994;171:1128.

Gardiner HM. Fetal echocardiography: 20 years of progress. Heart. 2001;86:II12.

National Institute of Child Health, Human Development Research Planning Workshop. Electronic fetal heart rate monitoring: research guidelines for interpretation. Am J Obstet Gynecol. 1997;177:1385.

Parer JT, King T. Fetal heart rate monitoring: is it salvageable? Am J Obstet Gynecol. 2000;182:982.

Parer JT, Livingston EG. What is fetal distress? Am J Obstet Gynecol. 1990;162:1421.

Samueloff A, Langer O, Berkus M, et al. Is fetal heart rate variability a good predictor of fetal outcome? Acta Obstet Gynecol Scand. 1994;73:39.

Schifrin BS. Fetal heart rate monitoring during labor. JAMA. 1972;222:196.

Sweha A, Hacker TW, Nuovo J. Interpretation of the electronic fetal heart rate during labor. Am Fam Physician. 1999;59:2487.

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