NeoReviews Vol.7 No.2 2006 e109
© 2006 American Academy of Pediatrics
Strip of the Month
February 2006
Maurice L. Druzin, MD*
Julie M.R. Arafeh, RN, MSN
* Charles B. and Ann L. Johnson Professor of Obstetrics; Chief, Division of Materna-Fetal Medicine; Co-Medical Director, Mid-Coastal California Perinatal Outreach Program, Stanford University School of Medicine, Palo Alto, Calif
Coordinator of Perinatal Outreach, Mid-Coastal California Perinatal Outreach Program, Stanford University, Palo Alto, Calif
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Electronic Fetal Monitoring Case Review Series
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Electronic fetal monitoring (EFM) is a popular technology used to establish fetal well-being. Despite its widespread use, terminology used to describe patterns seen on the monitor has not been consistent until recently. In 1997, the National Institute of Child Health and Human Development (NICHD) Research Planning Workshop published guidelines for interpretation of fetal tracings. This publication was the culmination of 2 years of work by a panel of experts in the field of fetal monitoring and has been endorsed by both the American College of Obstetricians and Gynecologists (ACOG) and the Association of Womens Health, Obstetric and Neonatal Nurses (AWHONN). The terminology definitions and assumptions found in the NICHD publication form the basis for interpretation of the fetal tracings in this series and are summarized here. Normal values for arterial umbilical cord gas values and indications of acidosis are defined in Table 1.
Table 1. Arterial Umbilical Cord Gas Values
|
pH |
PCO2 (mm Hg) |
PO2 (mm Hg) |
Base Excess |
|
| Normal* |
7.20 (7.15 to 7.38) |
<60 (35 to 70) |
20 |
10 (2.0 to 9.0) |
| Respiratory Acidosis |
<7.20 |
>60 |
Variable |
10 |
| Metabolic Acidosis |
<7.20 |
<60 |
Variable |
10 |
| Mixed Acidosis |
<7.20 |
>60 |
Variable |
10 |
|
* Normal ranges from Obstet Gynecol Clin North Am.1999;26:695
Assumptions from the NICHD Workshop
- Definitions are developed for visual interpretation
- Definitions apply to tracings generated by internal or external monitoring devices
- Periodic patterns are differentiated based on waveform, abrupt or gradual (eg, late decelerations have a gradual onset and variable decelerations have an abrupt onset)
- Long- and short-term variability are evaluated visually as a unit
- Gestational age of the fetus is considered when evaluating patterns
- Components of fetal heart rate (FHR) do not occur alone and generally evolve over time
Definitions
Baseline Fetal Heart Rate
- Approximate mean FHR rounded to increments of 5 beats/min in a 10-minute segment of tracing, excluding periodic or episodic changes, periods of marked variability, and segments of baseline that differ by >25 beats/min
- In the 10-minute segment, the minimum baseline duration must be at least 2 minutes or the baseline for that segment is indeterminate
- Bradycardia is a baseline of <110 beats/min; tachycardia is a baseline of >160 beats/min
- Sinusoidal baseline has a smooth sine wave-like pattern, with waves having regular frequency and amplitude
Baseline Variability
- Fluctuations in the baseline FHR of two cycles per minute or greater, fluctuations are irregular in amplitude and frequency, fluctuations are visually quantitated as the amplitude of the peak to trough in beats per minute
- Classification of variability: Absent: Amplitude range is undetectable Minimal: Amplitude range is greater than undetectable to 5 beats/min Moderate: Amplitude range is 6 to 25 beats/min Marked: Amplitude range is >25 beats/min
Accelerations
- Abrupt increase in FHR above the most recently determined baseline
- Onset to peak of acceleration is <30 seconds, acme is
15 beats/min above the most recently determined baseline and lasts
15 seconds but <2 minutes
- Before 32 weeks gestation, accelerations are defined by an acme
10 beats/min above the most recently determined baseline for
10 seconds
- Prolonged acceleration lasts
2 minutes but <10 minutes
Late Decelerations
- Gradual decrease in FHR (onset to nadir
30 seconds) below the most recently determined baseline, with nadir occurring after the peak of uterine contractions
- Considered a periodic pattern because it occurs with uterine contractions
Early Decelerations
- Gradual decrease in FHR (onset to nadir
30 seconds) below the most recently determined baseline, with nadir occurring coincident with uterine contraction
- Also considered a periodic pattern
Variable Decelerations
- Abrupt decrease in FHR (onset to nadir <30 seconds)
- Decrease is
15 beats/min below the most recently determined baseline lasting
15 seconds but <2 minutes
- May be episodic (occurs without a contraction) or periodic
Prolonged Decelerations
- Decrease in the FHR
15 beats/min below the most recently determined baseline lasting
2 minutes but <10 minutes from onset to return to baseline
Decelerations are tentatively called recurrent if they occur with
50% of uterine contractions in a 20-minute period.
We encourage readers to examine each strip in the case presentation and make a personal interpretation of the findings before advancing to the expert interpretation provided.
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Case Presentation
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History
A 29-year-old G 3 P 2002 woman presents to the labor and delivery unit at 39 2/7 weeks gestation with painful uterine contractions. Findings on personal, medical, and obstetrical histories are unremarkable. This pregnancy has been uncomplicated.
Progression of Labor
The woman is placed on EFM. The obstetrician who is in the labor room determines that the cervix is dilated 7 cm, and there is an increased amount of bloody show. EFM Strip #1 is shown in Figure 1.
Findings on EFM Strip #1 are: - Variability: Moderate
- Baseline rate: 110 to 120 beats/min
- Episodic Patterns: None
- Periodic Patterns: Prolonged deceleration
- Uterine contractions: Every 2 minutes lasting 40 seconds, with intensity and resting tone per palpation
- Interpretation: Reassuring due to the presence of moderate variability, but concerning because of the presence of prolonged deceleration
- Differential diagnosis: Umbilical cord occlusion
- Action: Turn the woman to the opposite side (right to left or left to right) to attempt to relieve occlusion due to position; prolapse of the cord should be ruled out during vaginal examination
Membranes are ruptured artificially, and slightly bloody amniotic fluid is noted. A fetal scalp electrode is placed. An anesthesia consult is obtained, and specimens for admission laboratory tests are drawn. Ten minutes later, EFM Strip #2 is obtained (Fig. 2).
Findings on EFM Strip #2 are: - Variability: Moderate
- Baseline rate: 120 beats/min
- Episodic patterns: Variable decelerations
- Periodic patterns: None
- Uterine contractions: Every 2 minutes lasting 40 to 80 seconds, with intensity and resting tone per palpation
- Interpretation: Reassuring because of the presence of moderate variability, but persistent variable decelerations remain concerning
- Differential diagnosis: Umbilical cord occlusion versus early abruption due to bloody amniotic fluid
- Action: Assess maternal hemodynamic parameters noninvasively for signs of hypovolemia
Because of the persistent decelerations, the patient is moved to the operating room emergently for potential cesarean delivery. Ten minutes later, EFM Strip #3 is obtained (Fig. 3).
Findings on EFM Strip #3 are: - Variability: Moderate
- Baseline rate: 120 to 130 beats/min
- Episodic patterns: Variable decelerations
- Periodic patterns: Unable to determine because uterine contractions not present
- Uterine contractions: Unable to determine
- Interpretation, differential diagnosis, and action: Unchanged
Evaluation of the cervix in the operating room reveals that cervical dilation is complete, effacement is complete, and the presenting part is at -1 station. A spinal epidural is placed for pain management. Ten minutes later, EFM Strip #4 is obtained (Fig. 4).
Findings on EFM Strip #4 are: - Variability: Minimal
- Baseline rate: 50 to 60 beats/min (bradycardia)
- Episodic patterns: None
- Periodic patterns: None
- Uterine contractions: Unable to determine
- Interpretation: Fetal stress
- Differential diagnosis: Umbilical cord occlusion versus progressing abruption
- Action: Briefly attempt to reposition the woman to relieve cord compression and assess for hypotension due to placement of spinal anesthesia. An FHR of 60 beats/min or less is associated with absent fetal perfusion; emergent delivery is necessary if the FHR does not respond to repositioning or if hypotension, if present, is not corrected rapidly
Outcome
A viable female infant weighing 3,304 g is delivered by emergent cesarean section due to a low FHR that did not respond to intrauterine resuscitative actions (position change, correction of hypotension). Nuchal cord x 2, thick meconium, and placenta suspicious for abruption are noted at delivery. Apgar scores are 6 at 1 minute and 8 at 5 minutes. The infant is resuscitated with suction, oxygen, and intubation. She is admitted to the well baby nursery. Arterial cord gas findings in relation to normal findings and those of acidosis are shown in Table 2.
Table 2. Arterial Umbilical Cord Gas Values
|
pH |
PCO2 (mm Hg) |
PO2 (mm Hg) |
Base Excess |
|
| Normal* |
7.20 (7.15 to 7.38) |
<60 (35 to 70) |
20 |
10 (2.0 to 9.0) |
| Respiratory Acidosis |
<7.20 |
>60 |
Variable |
10 |
| Metabolic Acidosis |
<7.20 |
<60 |
Variable |
10 |
| Mixed Acidosis |
<7.20 |
>60 |
Variable |
10 |
| Patient |
7.13 |
80 |
9 |
2.6 |
|
* Normal ranges from Obstet Gynecol Clin North Am.1999;26:695
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Footnotes
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Author Disclosure
Dr Druzin and Ms Arafeh did not disclose any financial relationships relevant to this article.
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Suggested Reading
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ACOG Practice Bulletin #62.
Intrapartum Fetal Heart Rate Monitoring.May 2005.Freeman RK. Problems with intrapartum fetal heart rate monitoring interpretation and patient management.
Obstet Gynecol. 2002;100
:813
826[Abstract/Free Full Text]
National Institute of Child Health and Human Development Research Planning Group. Electronic fetal heart rate monitoring: research guidelines for interpretation.
Am J Obstet Gynecol. 1997;177
:1385
1390.[Medline]