What are the management steps for a primigravida (first-time pregnant woman) at 36+4 weeks of gestation with a fetal heart rate (FHR) that has increased from the 140's to between 160 and 190 beats per minute (bpm)?

Management of Fetal Tachycardia at 36+4 Weeks

This fetal heart rate of 160-190 bpm represents fetal tachycardia (>160 bpm) and requires immediate evaluation with continuous electronic fetal monitoring to assess baseline variability, presence of decelerations, and overall fetal well-being, followed by investigation of maternal and fetal causes. 1

Immediate Assessment Steps

Obtain continuous electronic fetal monitoring immediately to properly classify this tracing using the NICHD three-category system and determine urgency of intervention. 1, 2

Critical Parameters to Evaluate

• Assess baseline FHR variability: Moderate variability (6-25 bpm) is reassuring and predicts absence of fetal acidemia, while absent variability combined with tachycardia is concerning. 1, 2

• Check for decelerations: The presence of recurrent late or variable decelerations with absent variability would classify this as Category III (abnormal), requiring immediate delivery. 1, 2

• Evaluate maternal vital signs: Check temperature, blood pressure, and pulse to identify maternal fever, infection, or hyperthyroidism as potential causes of fetal tachycardia. 1

• Perform vaginal examination: Assess cervical status and rule out cord prolapse or rapid descent. 1

Determine NICHD Category Classification

If Category II (Indeterminate) - Tachycardia with Moderate Variability

• This is the most likely scenario and represents an indeterminate tracing requiring investigation of underlying causes. 1

• Investigate maternal causes: Fever, infection (chorioamnionitis), maternal anxiety, medications (beta-agonists, terbutaline), or maternal hyperthyroidism. 1

• Implement general measures: Change maternal position to left lateral, administer oxygen at 6-10 L/min, give IV fluid bolus, and discontinue oxytocin if being administered. 1, 3

• Consider expedited delivery if abnormalities persist despite interventions or if pattern worsens. 1

If Category III (Abnormal) - Tachycardia with Absent Variability and Decelerations

• Discontinue oxytocin immediately if being administered. 1, 2

• Expedite delivery by operative vaginal delivery or cesarean section without delay, as this represents fetal hypoxia or acidemia. 1, 2

Differential Diagnosis and Workup

At 36+4 weeks gestation, consider both maternal and fetal causes:

Maternal Causes to Investigate

• Maternal fever/infection: Check temperature and consider chorioamnionitis if fever present with uterine tenderness. 1

• Medications: Review recent administration of beta-agonists, terbutaline, or other medications that increase FHR. 1

• Maternal hyperthyroidism: Consider if history suggests thyroid disease. 1

Fetal Causes to Consider

• Fetal arrhythmia: Supraventricular tachycardia (SVT) typically presents with sustained rates of 220-280 bpm with 1:1 conduction, which is higher than this case. 4

• Fetal anemia: Less likely without other signs, but consider if history of isoimmunization or infection. 1

• Fetal hypoxia: Tachycardia can be an early compensatory response to hypoxia before development of late decelerations. 1

Management Algorithm Based on Findings

If Maternal Fever/Infection Identified

• Administer broad-spectrum antibiotics for suspected chorioamnionitis. 1

• Continue continuous fetal monitoring and prepare for delivery if FHR pattern worsens or labor progresses. 1

• Expect FHR to normalize as maternal temperature decreases with treatment. 1

If No Clear Cause Identified and Tracing Remains Category II

• Continue continuous electronic fetal monitoring with reassessment every 15-30 minutes. 1

• Consider delivery at 37 weeks given near-term gestation (currently 36+4 weeks), especially if pattern persists or worsens. 1

• Do not delay delivery beyond 37 weeks if tachycardia persists without clear reversible cause. 1

If True Fetal Arrhythmia Suspected (Sustained Rate >200 bpm)

• Obtain fetal echocardiography to evaluate for structural heart disease and confirm arrhythmia type. 5, 4

• At 36+4 weeks gestation, delivery and postnatal treatment is preferred over transplacental antiarrhythmic therapy, which is typically reserved for fetuses <36 weeks. 4

Critical Pitfalls to Avoid

• Do not assume this is normal variation: A baseline FHR of 160-190 bpm exceeds the normal range of 110-160 bpm and requires investigation. 1, 6

• Do not rely on intermittent auscultation alone: Continuous electronic monitoring is essential to assess variability and detect decelerations. 1

• Do not delay evaluation: At 36+4 weeks, the fetus is near-term and delivery may be the safest option if concerning features develop. 1

• Do not confuse fetal sleep cycles with pathologic absent variability: Sleep cycles last 20-40 minutes and should resolve spontaneously, whereas persistent absent variability with tachycardia is pathologic. 1, 2

Delivery Considerations

Given gestational age of 36+4 weeks, have a low threshold for delivery if:

• Pattern progresses to Category III (absent variability with decelerations). 1, 2

• Maternal infection/fever persists despite treatment with worsening fetal status. 1

• No reversible cause identified and tachycardia persists beyond 37 weeks gestation. 1