Electronic fetal monitoring (EFM) is a popular technology used to establish fetal well-being. Despite its widespread use, the 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 was endorsed in 2005 by both the American College of Obstetricians and Gynecologists (ACOG) and the Association of Women’s Health, Obstetric and Neonatal Nurses (AWHONN). In 2008, ACOG, NICHD, and the Society for Maternal-Fetal Medicine reviewed and updated the definitions for fetal heart rate (FHR) patterns, interpretation, and research recommendations. Following is a summary of the terminology definitions and assumptions found in the 2008 NICHD workshop report. Normal arterial umbilical cord gas values and indications of acidosis are defined in the Table.Definitions are developed for visual interpretation, assuming that both the FHR and uterine activity recordings are of adequate qualityDefinitions 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 unitGestational age of the fetus is considered when evaluating patternsComponents of FHR do not occur alone and generally evolve over timeApproximate mean FHR rounded to increments of 5 beats/min in a 10-minute segment of tracing, excluding accelerations and decelerations, periods of marked variability, and segments of baseline that differ by >25 beats/minIn the 10-minute segment, the minimum baseline duration must be at least 2 minutes (not necessarily contiguous) or the baseline for that segment is indeterminateBradycardia is a baseline of <110 beats/min; tachycardia is a baseline of >160 beats/minSinusoidal baseline has a smooth sine wave-like undulating pattern, with waves having regular frequency and amplitudeFluctuations in the baseline FHR of ≥2 cycles per minute, fluctuations are irregular in amplitude and frequency, fluctuations are visually quantitated as the amplitude of the peak to trough in beats per minuteClassification of variability:Absent: Amplitude range is undetectableMinimal: Amplitude range is greater than undetectable to 5 beats/minModerate: Amplitude range is 6–25 beats/minMarked: Amplitude range is >25 beats/minAbrupt increase in FHR above the most recently determined baselineOnset to peak of acceleration is <30 seconds, acme is ≥15 beats/min above the most recently determined baseline and lasts ≥15 seconds but <2 minutesBefore 32 weeks’ gestation, accelerations are defined by an acme ≥10 beats/min above the most recently determined baseline for ≥10 secondsProlonged acceleration lasts ≥2 minutes but <10 minutesGradual decrease in FHR (onset to nadir ≥30 seconds) below the most recently determined baseline, with nadir occurring after the peak of uterine contractionsConsidered a periodic pattern because it occurs with uterine contractionsGradual decrease in FHR (onset to nadir ≥30 seconds) below the most recently determined baseline, with nadir occurring coincident with uterine contractionAlso considered a periodic patternAbrupt decrease in FHR (onset to nadir <30 seconds)Decrease is ≥15 beats/min below the most recently determined baseline lasting ≥15 seconds but <2 minutesMay be episodic (occurs without a contraction) or periodicDecrease in the FHR ≥15 beats/min below the most recently determined baseline lasting ≥2 minutes but <10 minutes from onset to return to baselineDecelerations are tentatively called recurrent if they occur with ≥50% of uterine contractions in a 20-minute periodDecelerations occurring with <50% of uterine contractions in a 20-minute segment are intermittentVisually apparent, smooth sine wave-like undulating pattern in the baseline with a cycle frequency of 3 to 5 per minute that persists for ≥20 minutesQuantified as the number of contractions in a 10-minute window, averaged over 30 minutes Normal: ≤5 contractions in 10 minutesTachysystole: >5 contractions in 10 minutesA 3-tier FHR interpretation system has been recommended as follows: Category I FHR tracings: Normal, strongly predictive of normal fetal acid-base status and require routine care. These tracings include all of the following: − Baseline rate: 110 to 160 beats/min− Baseline FHR variability: Moderate− Late or variable decelerations: Absent− Early decelerations: Present or absent− Accelerations: Present or absentCategory II FHR tracings: Indeterminate, require evaluation and continued surveillance and reevaluation. Examples of these tracings include any of the following: − Bradycardia not accompanied by absent variability− Tachycardia− Minimal or marked baseline variability− Absent variability without recurrent decelerations− Absence of induced accelerations after fetal stimulation− Recurrent variable decelerations with minimal or moderate variability− Prolonged decelerations− Recurrent late decelerations with moderate variability− Variable decelerations with other characteristics, such as slow return to baselineCategory III FHR tracings: Abnormal, predictive of abnormal fetal acid-base status and require prompt intervention. These tracings include: − Absent variability with any of the following: ▪ Recurrent late decelerations▪ Recurrent variable decelerations▪ Bradycardia− Sinusoidal patternData from Macones GA, Hankins GDV, Spong CY, Hauth J, Moore T. The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring. Obstet Gynecocol. 2008;112:661–666 and American College of Obstetricians and Gynecologists. Intrapartum fetal heart rate monitoring: nomenclature, interpretation, and general management principles. ACOG Practice Bulletin No. 106. Washington, DC: American College of Obstetricians and Gynecologists; 2009.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.Four days after symptom onset, a 36-year-old, unvaccinated, gravida 2, para 1-0-0-1 woman presented to her local emergency department (ED) at 35 weeks and 5 days’ gestation with shortness of breath, nausea, and vomiting. She tested positive for COVID-19 on a polymerase chain reaction (PCR) nasal swab. Her pregnancy was complicated by untreated hepatitis C (viral load at the time of admission 76 IU/mL), class II obesity, and mild persistent asthma. In the month prior to her infection, ultrasonography findings were consistent with a well-grown fetus and normal amniotic fluid. Her obstetrical history included an uncomplicated full-term vaginal delivery. Her evaluation included computed tomography angiography without pneumonia or pulmonary embolism. After her ED evaluation, she was discharged from the hospital for outpatient management. Her 11-year-old son and partner were also symptomatic with PCR test–confirmed COVID-19 infections.Five days later, now 9 days after symptom onset, she presented to her local ED again with progressive shortness of breath. Her laboratory findings were notable for an anion gap metabolic acidosis (bicarbonate level of 9 mEq/L [9 mmol/L], anion gap of 17, and no initial pH), for which she was hydrated and transferred to an obstetric/medicine care unit. On the 10th day after symptom onset, she became increasingly hypoxemic, requiring 5 L of oxygen via nasal cannula to maintain pulse oxygen saturations between 93% and 95%. Arterial blood gas measurement confirmed persistent metabolic acidosis despite hydration (pH 7.26, bicarbonate 12 mEq/L [12 mmol/L]). Chest radiography demonstrated left lower lobe consolidations with concern for superimposed bacterial pneumonia. She was started on azithromycin, remdesivir, and dexamethasone and symptomatically treated with ondansetron, metoclopramide, and acetaminophen. Tertiary care referral and transfer to our facility was initiated for intensive care unit access for maternal and neonatal care.At the time of admission to our facility, the patient was receiving 4 L of oxygen via nasal cannula, with a pulse oxygen saturation between 97% and 99%. She was tachycardic to 110 beats/min, with a pulmonary examination notable for bilateral upper lobe coarse breath sounds, bilateral lower lobe decreased breath sounds, and tachypnea with a respiratory rate of 28 breaths/min. Laboratory evaluation was remarkable for a bicarbonate level of 10 mEq/L (10 mmol/L) with an anion gap of 20. β-hydroxybutyrate was elevated at 5.2 mmol/L (93.6 mg/dL or 0.0052 mol/L), C-reactive protein was elevated at 7.99 mg/dL (79.9 mg/L), and D-dimer was significantly elevated at 6,174 μg/L (6.174×10−6 g/mL or 19,633 nmol/L).Upon arrival, an initial arterial blood gas was notable for metabolic acidosis with a pH of 7.32, partial pressure of oxygen of 108 mm Hg (14.3 kPa), partial pressure of carbon dioxide of 17 mm Hg (2.2 kPa), bicarbonate of 8 mEq/L (8 mmol/L), and base deficit of 16. Her overall clinical status was consistent with severe COVID-19 infection with starvation metabolic acidosis. She continued to receive dexamethasone, remdesivir, and antibiotics for community-acquired pneumonia and intravenous fluids with dextrose. Bedside fetal ultrasonography confirmed normal amniotic fluid and vertex fetal presentation. A representative FHR tracing at the time of transfer is included in Fig 1.Interpretation of Fig 1: Variability: ModerateBaseline rate: 150 beats/minAccelerations: YesEpisodic patterns: NonePeriodic patterns: NoneUterine contractions: Every 2 minutesInterpretation: Category IDifferential diagnosis: Possible relative fetal tachycardia, dehydration, hypoxiaAction: Ongoing assessment of maternal and fetal clinical statusThe patient required ongoing inpatient treatment for hypoxemia and persistent metabolic acidosis. The patient was within the peak window from symptom onset (10–14 days), when her risk of decompensation from inflammatory response was most likely. Her metabolic derangement was thought to be starvation ketosis, given the ketonuria noted on admission (150 ketones mg/dL on urinalysis) and minimal oral intake for approximately 1 week before hospitalization. Other etiologies, such as euglycemic diabetic ketoacidosis, alcohol use, and aspirin toxicity, were excluded. The neonatology and anesthesia teams were notified, given the potential need to move toward delivery at a greater preterm gestational age. She remained in the labor and delivery department for prolonged monitoring. A follow-up fetal assessment on the morning after admission is represented in Fig 2.Interpretation of Fig 2: Variability: MinimalBaseline rate: 155 beats/minAccelerations: AbsentEpisodic patterns: NonePeriodic patterns: NoneUterine contractions: NoneInterpretation: Category IIDifferential diagnosis: Normal fetal status (sleep cycle), fetal hypoxia, abruption.Action: Intervention included ongoing COVID-19 treatment, fluids, ensuring adequate maternal oxygenation, and maternal repositioning for intrauterine resuscitationOn the day after admission (11 days after symptom onset), her oxygen requirement decreased, her tachypnea improved, and the anion gap metabolic acidosis improved; however, she continued to require oxygen. A representative FHR tracing is seen in Fig 3.Interpretation of Fig 3: Variability: ModerateBaseline rate: 125 beats/minAccelerations: PresentEpisodic patterns: NonePeriodic patterns: NoneUterine contractions: Occasional sporadic.Interpretation: Category IDifferential diagnosis: Improved maternal/fetal statusAction: Given overall clinical improvement, continuous fetal monitoring was changed to intermittent fetal monitoring; the patient was transferred to our antepartum floorDespite initial improvement, the next evening, the patient’s respiratory status declined and her oxygen requirement increased to 8 L via cannula. Repeat chest radiography showed progression of multifocal opacities consistent with worsening COVID-19 pneumonia. Given her respiratory decompensation and late preterm gestational age at 36 weeks and 4 days’ gestation, delivery was advised. An induction of labor was initiated. During her induction course, the patient’s respiratory status worsened. The intrapartum FHR tracing is shown in Fig 4:Interpretation of Fig 4: Variability: Minimal-moderate variabilityBaseline rate: 150 beats/minAccelerations: AbsentEpisodic patterns: Late decelerations to 140 beats/minPeriodic patterns: NoneUterine contractions: Every 2 minutesInterpretation: Category IIDifferential diagnoses: Fetal acidosis secondary to worsening maternal respiratory status, uteroplacental insufficiencyAction: Stabilization of maternal oxygenation statusThe fetal tracing improved after optimization of maternal oxygenation status with an increase to 10 L nonrebreather face mask. The induction continued. She progressed to becoming fully dilated. With pushing, the patient’s oxygen level dropped to 89% on 12 L via cannula. Her oxygen supplementation was then transitioned to high-flow oxygen with improvement in oxygen saturations to 95%. A representative FHR tracing during this period of desaturation before delivery is shown in Fig 5.Interpretation of Fig 5: Variability: ModerateAccelerations: AbsentBaseline rate: 150 beats/minEpisodic patterns: Variable decelerations without recovery to baselinePeriodic patterns: NoneUterine contractions: Every 2 minutesInterpretation: Category IIDifferential diagnosis: Fetal acidosis from deteriorating maternal respiratory status, uteroplacental insufficiencyAction: Expedite delivery with operative assisted vaginal delivery if delivery is not imminentAfter a short second stage of labor, the patient had a vaginal delivery of a liveborn male infant weighing 3,550 g with Apgar scores of 8 and 9 at 1 and 5 minutes, respectively. Neonatology staff was present in the delivery room and the newborn was transferred to the NICU for monitoring. Immediately after delivery, the patient’s respiratory status improved, with reduced oxygen requirement. She was eventually transitioned back to minimal oxygen support via nasal cannula at the time of transfer to the postpartum floor. On postpartum day 6, she was weaned to room air.The infant continued to be monitored in the NICU. As both parents were COVID-19 positive, neither was able to visit the infant in the NICU. The infant had a negative COVID-19 swab on day 2 after birth and was reunited with his parents in the postpartum room at that time.Our case describes a pregnant woman with severe COVID-19 pneumonia and hypoxemia resulting in significant maternal and fetal morbidity. FHR monitoring can help determine the oxygenation status of the fetus. (1) However, there is limited information regarding whether maternal COVID-19 infection has any effect on FHR tracing. A study of 224 pregnant women infected with COVID-19 demonstrated no statistically significant relationship between the severity of infection and any FHR pattern or Apgar scores. (2) Similar to other maternal disease states, the FHR tracing in this case improved after maternal respiratory stabilization.Available data suggest that COVID-19 infection in and of itself is not an indication for delivery; expedited delivery should be evaluated on a case-by-case basis with consideration of gestational age, current maternal status, the maternal disease course, and anticipated progression. (3)(4) Data suggest a severity peak in the second week of maternal illness. (3)(5) If respiratory compromise is significant despite maximizing treatment modalities, a preterm delivery may be considered. (4)(6)(7) Data on pregnant women with severe COVID-19 and acute respiratory distress syndrome are limited; some retrospective studies indicate that delivery may improve the maternal respiratory status of pregnant women with acute respiratory failure. (8)(9) Although the threshold for cesarean delivery may be lower in patients with COVID-19 pneumonia, COVID-19 infection is not a contraindication to vaginal delivery. (4)(10)Although COVID-19 infection is associated with maternal morbidity, the risks to the fetus or neonate are somewhat limited. Currently available data indicate that vertical transmission appears to be uncommon. (10)(11)(12) In 9,500 cases in the Perinatal COVID-19 Registry, approximately 2% of infants tested positive for COVID-19 in the first 24 to 96 hours after birth to pregnant women infected with COVID-19. (11)(13) The risk of infection to newborns is highest when a pregnant women has onset of COVID-19 near the time of delivery. (13)(14)Recommendations regarding the need for physical separation of newborns from their mother with COVID-19 have evolved during the pandemic. Data continue to suggest that neonatal COVID-19 infection is uncommon, rarely symptomatic, and the rate of infection is not increased when the neonate is born vaginally, breastfed, or remains with the mother. Currently American Academy of Pediatrics guidance recommends avoiding separation of the mother and newborn unless the maternal status prohibits care of the newborn. (15)(16) As with our patient, the neonate needed ongoing support in the NICU and the parents were unable to visit due to their positive status. Once the neonate was discharged from the NICU and sufficiently stable for the regular nursery, our patient was reunited with her newborn in her postpartum room.This case demonstrates the implications of maternal respiratory status on fetal status. Delivery timing of a pregnancy affected by severe COVID-19 pneumonia needs to be individualized. For our patient, the maternal status significantly worsened at a late preterm gestation and delivery was recommended. Fortunately, despite severe COVID-19 infection in an unvaccinated patient, the outcome was reassuring.
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