A 26-year-old woman, gravida 1 para 0, is evaluated in the labor and delivery unit at 40 w… — USMLE Step 2 CK

A 26-year-old woman, gravida 1 para 0, is evaluated in the labor and delivery unit at 40 weeks and 2 days of gestation. She was admitted 6 hours ago in active labor. Her prenatal course was uncomplicated. Admission laboratory values demonstrated a hemoglobin concentration of $10.4\text{ g/dL}$ and a leukocyte count of $11,500/\mu\text{L}$ . Epidural analgesia was administered, and an artificial rupture of membranes was performed at 5 centimeters of cervical dilation, yielding clear fluid.

Currently, the patient's blood pressure is $118/76\text{ mmHg}$ , pulse is $84/\text{min}$ , and temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ). Uterine contractions occur every 3 to 4 minutes, lasting 50 seconds, with normal intensity upon palpation. Cervical examination reveals 8 centimeters of dilation, 100% effacement, and the fetal vertex at 0 station. Fetal monitoring demonstrates a baseline heart rate of $150/\text{min}$ with moderate variability and no accelerations. Over the last 40 minutes, the cardiotocograph has shown abrupt decreases in the fetal heart rate to $80/\text{min}$ , lasting 45 to 60 seconds before rapidly returning to baseline. These decreases are noted during approximately 60% of the uterine contractions. Maternal repositioning to the left lateral decubitus position, an intravenous normal saline bolus, and supplemental oxygen administration have been implemented, but the fetal heart rate pattern remains unchanged.

Which of the following is the most appropriate next step in the management of this patient?

Transcervical amnioinfusionAnswer
B
Emergent Cesarean delivery
C
Administration of a uterine tocolytic agent
D
Forceps-assisted vaginal delivery
E
Transfusion of packed red blood cells

Answer

Transcervical amnioinfusion

The correct management for recurrent variable decelerations that do not respond to initial intrauterine resuscitation (maternal repositioning, intravenous fluids, oxygen) is transcervical amnioinfusion. Variable decelerations—characterized by an abrupt drop in the fetal heart rate—are caused by umbilical cord compression. This frequently occurs after the rupture of membranes due to the loss of protective amniotic fluid volume (oligohydramnios). By instilling an isotonic fluid (such as normal saline) into the uterine cavity through an intrauterine pressure catheter, amnioinfusion restores the fluid buffer around the umbilical cord and typically resolves the decelerations. Because the fetal heart rate currently demonstrates moderate variability, the tracing is considered Category II (indeterminate but lacking evidence of fetal acidemia). This provides the obstetrician time to attempt amnioinfusion before resorting to surgical intervention. If amnioinfusion fails to resolve the decelerations, or if the tracing deteriorates to Category III (e.g., absent variability with recurrent decelerations), prompt delivery would then be indicated.

Step-by-Step Solution

Analyze the fetal heart rate tracing to identify the specific abnormality.

The tracing shows recurrent variable decelerations (abrupt decreases of

\geq 15

beats/min lasting

\geq 15

seconds, occurring with

\geq 50\%

of contractions).

Variable decelerations are typically caused by umbilical cord compression, which frequently occurs after rupture of membranes.

Determine the current category of the fetal heart rate tracing to assess for fetal acidemia.

The tracing is Category II because it maintains moderate variability despite the deep decelerations.

Moderate variability strongly predicts a normal fetal acid-base status, meaning emergent surgical delivery is not immediately indicated.

Evaluate the response to initial intrauterine resuscitation measures.

Maternal repositioning, an intravenous fluid bolus, and supplemental oxygen failed to resolve the decelerations.

When first-line maneuvers fail to relieve cord compression in a Category II tracing, the next algorithmic step is required to actively resolve the compression.

Select the most appropriate intervention for unresolved recurrent variable decelerations.

Transcervical amnioinfusion is selected.

Instilling isotonic fluid into the uterine cavity cushions the umbilical cord, relieving the compression and often resolving the decelerations, which safely prevents an unnecessary Cesarean delivery.

Key Concept

The management of recurrent variable decelerations in labor involves initial intrauterine resuscitation (repositioning, fluids, oxygen) followed by transcervical amnioinfusion if the decelerations persist and the fetal heart rate tracing remains Category II (moderate variability).

Estimated Time:1m 15s

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