II. Classification of FHT Variability
- Absent variability
- Minimal variability (<5 bpm change)
- Moderate variability (6 to 25 bpm change)
- Marked variability (>25 bpm change)
III. Evaluation
- Continuous monitoring
IV. Interpretation
- Normally FHR varies 10-15 bpm from baseline
- Variability is related to fetal cerebral activity
- Evaluation based on one of two techniques
- Continuous Electronic Fetal Monitoring (CEFM)
- Structured Intermittent Auscultation (SIA)
- Count FHR in five second intervals over 60 seconds
- Examples (12 number sets)
- Good: 10,12,13,12,10,12,13,11,11,13,12,13
- Poor: 11,11,10,11,11,11,11,10,10,10,11,10
V. Efficacy: Loss of Variability
- Most accurate with internal scalp electrode
- Low sensitivity: 17%
- High Specificity
- Reassuring if normal variability
- Most specific for fetal asphyxia
- Negative Predictive Value >98%
VI. Causes: Decreased FHT Variability
- Normal causes
- Fetal sleep cycle (usually lasts 20-40 minutes)
- Extreme prematurity
- Medications
- Opioids
- Benzodiazepines
- Anticholinergic Medications
- Barbiturates
- Phenothiazines
- Parasympatholytic medications
- General Anesthesia
- Maternal Cocaine use
- Magnesium Sulfate
- Betamethasone (does not occur with Dexamethasone)
-
Fetal Hypoxia or Metabolic Acidosis
- Especially concerning if other findings of distress
- Associated with decreased APGAR Scores if uncorrected
- Other abnormal causes
- Fetal neurologic anomalies (Anencephaly)
- Chorioamnionitis
- Fetal Heart Block
- Fetal Tachycardia
VII. References
- Bailey (2000) ALSO, E:1-13
- Gabbe (2002) Obstetrics, p. 395
- Arnold (2020) Am Fam Physician 102(3): 158-67 [PubMed]
- Rylander (2001) Clin Fam Pract 3(2):287-305 [PubMed]