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Question

Difficulty: MediumLabor, Delivery, and Puerperium

A nulliparous woman presents to the labor ward at 40 weeks of gestation complaining of regular, painful contractions. Upon admission, her vital signs are within normal limits. Her cervix is dilated to 5 cm and is 90% effaced. Artificial rupture of membranes is performed, yielding a moderate amount of clear amniotic fluid. Two hours later, her cervix is 7 cm dilated. The continuous fetal heart rate tracing demonstrates a baseline of 140/min and moderate variability. However, the tracing also reveals recurrent, abrupt drops in the heart rate to 90/min that last for 40 seconds before rapidly returning to the baseline. These drops are not consistently related to the peak of the uterine contractions, which are occurring every 3 minutes. The patient is immediately placed in the left lateral decubitus position and given an intravenous fluid bolus, but the fetal heart rate pattern remains unchanged. Which of the following is the most appropriate next step in management?

  1. Initiate an amnioinfusionAnswer
  2. B
    Proceed to cesarean delivery
  3. C
    Administer terbutaline
  4. D
    Continue expectant management
  5. E
    Apply a fetal scalp electrode

Answer

The correct answer is to initiate an amnioinfusion.
This patient is experiencing recurrent variable decelerations, which are characterized by abrupt decreases in the fetal heart rate (onset to nadir in less than 30 seconds) that drop at least 15/min below baseline and last for at least 15 seconds. These decelerations are caused by umbilical cord compression, which frequently occurs or worsens after the rupture of membranes due to the loss of protective amniotic fluid. When initial intrauterine resuscitative maneuvers (such as maternal repositioning and intravenous fluid boluses) fail to alleviate the cord compression, the most appropriate next step is to initiate an amnioinfusion. Amnioinfusion involves the transcervical instillation of normal saline or lactated Ringer's solution into the uterine cavity. This procedure artificially replenishes the amniotic fluid volume, cushions the umbilical cord, and typically resolves the variable decelerations, thereby reducing the likelihood of fetal acidemia and the need for a cesarean delivery.

Step-by-Step Solution

1
Interpret the fetal heart rate tracing abnormalities.
The tracing demonstrates recurrent variable decelerations (abrupt decreases in heart rate lasting less than 2 minutes) occurring independently of contractions.
Accurate interpretation of the fetal heart rate pattern dictates the etiology, which in this case is umbilical cord compression exacerbated by the recent artificial rupture of membranes.
2
Evaluate the response to initial intrauterine resuscitative measures.
The patient has already received maternal repositioning and an intravenous fluid bolus without improvement in the decelerations.
Determining if first-line interventions have been exhausted is necessary before escalating treatment.
3
Determine the next pharmacological or mechanical intervention.
Amnioinfusion is indicated.
Instilling isotonic fluid into the uterine cavity artificially restores amniotic fluid volume, cushions the umbilical cord, and often resolves persistent variable decelerations.

Key Concept

Management of recurrent variable decelerations requires stepwise intrauterine resuscitation starting with maternal repositioning and fluid administration; if unsuccessful, amnioinfusion is the definitive medical treatment to relieve umbilical cord compression.
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Topics

Labor, Delivery, and Puerperium

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