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Difficulty: HardLabor, Delivery, and Puerperium

An uncomplicated first-time mother, 22 years of age, is evaluated in the labor and delivery ward at term (38 weeks and 5 days). She was admitted earlier today in spontaneous labor. Her membranes ruptured naturally two hours ago with clear fluid noted. Her current vital signs are within normal limits.

Pelvic examination reveals a cervix that is 7 cm dilated and fully effaced, with the fetal vertex at 0 station. An internal intrauterine pressure catheter and a fetal scalp electrode are placed. Contractions are adequate, occurring every 3 minutes and lasting 60 seconds.

Review of the electronic fetal monitoring tracing over the past 30 minutes shows a baseline heart rate of 135/min with moderate beat-to-beat variability. Frequent, sudden drops in the fetal heart rate to 75/min are observed. These drops reach their nadir in less than 30 seconds, last for approximately 45 seconds, and are not consistently synchronized with the onset of uterine contractions.

Nursing staff has already assisted the patient into a left-lateral resting position and administered a 500 mL intravenous bolus of lactated Ringer's, yet the fetal heart rate pattern persists without improvement.

Based on the clinical presentation, which of the following is the most appropriate next step in management?

  1. Initiate an amnioinfusionAnswer
  2. B
    Proceed to an emergency cesarean delivery
  3. C
    Administer a dose of subcutaneous terbutaline
  4. D
    Perform fetal scalp blood sampling
  5. E
    Continue routine monitoring without intervention

Answer

Initiate an amnioinfusion
The correct answer is to initiate an amnioinfusion. The patient is experiencing recurrent variable decelerations, which are defined by abrupt decreases in the fetal heart rate (onset to nadir of < 30 seconds) that are not consistently timed with uterine contractions. These are primarily caused by umbilical cord compression, which is common following the rupture of membranes. When first-line intrauterine resuscitative measures—such as maternal repositioning (to relieve caval compression and alter cord position) and intravenous fluid boluses—fail to resolve the decelerations, an amnioinfusion is the next best step. This procedure involves instilling normal saline or lactated Ringer's into the uterine cavity via an intrauterine pressure catheter to artificially restore amniotic fluid volume, cushion the umbilical cord, and alleviate the compression.

Step-by-Step Solution

1
Interpret the fetal heart rate (FHR) tracing from the clinical description.
The tracing shows abrupt decreases in FHR (onset to nadir in <30 seconds) that drop 15 or more beats/min and last 15 or more seconds, which defines variable decelerations.
Accurate identification of the deceleration pattern is required to determine the underlying etiology.
2
Correlate the deceleration pattern with its physiologic cause.
Variable decelerations are caused by umbilical cord compression, often exacerbated by oligohydramnios or rupture of membranes.
Management must be tailored to the specific pathophysiology of the FHR abnormality.
3
Evaluate the response to initial resuscitative interventions.
The patient has already received first-line conservative management (left-lateral repositioning and an intravenous fluid bolus) without resolution of the decelerations.
Persistent recurrent variable decelerations require an escalation of therapy to prevent fetal acidemia.
4
Determine the most appropriate next therapeutic step.
Amnioinfusion is indicated.
Instilling saline into the uterine cavity artificially replaces amniotic fluid, thereby cushioning the umbilical cord and directly relieving the compression.

Key Concept

Recurrent variable decelerations are caused by umbilical cord compression and are managed first with maternal repositioning, followed by amnioinfusion if initial measures fail.
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Topics

Labor, Delivery, and Puerperium

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