A 25-year-old primigravida at 41 weeks gestation is admitted to the labor and delivery uni… — USMLE Step 2 CK

A $25$ -year-old primigravida at $41$ weeks gestation is admitted to the labor and delivery unit for induction of labor due to postterm pregnancy. A continuous intravenous oxytocin infusion is initiated. Her cervix is $5\text{ cm}$ dilated and $80\%$ effaced. Uterine contractions are occurring every $3$ to $4$ minutes. The fetal heart rate baseline is $135/\text{min}$ with moderate variability. Over the past $30$ minutes, the fetal heart rate tracing demonstrates recurrent, symmetric decreases in the heart rate that begin after the peak of each contraction, reach their nadir after the contraction ends, and then gradually return to baseline. Maternal vital signs are temperature $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure $118/76\text{ mmHg}$ , and heart rate $84/\text{min}$ . Laboratory studies show a leukocyte count of $14,500/\text{mm}^3$ and hemoglobin of $10.8\text{ g/dL}$ . Which of the following is the most appropriate next step in management?

Discontinuation of oxytocin infusion and maternal repositioningAnswer
B
Immediate cesarean delivery
C
Prophylactic amnioinfusion
D
Subcutaneous terbutaline administration
E
Intravenous administration of broad-spectrum antibiotics

Answer

Discontinuation of oxytocin infusion and maternal repositioning

The patient's fetal heart rate tracing demonstrates late decelerations, which are defined as visually apparent, gradual decreases in the fetal heart rate where the nadir of the deceleration occurs after the peak of the uterine contraction. Recurrent late decelerations are a sign of uteroplacental insufficiency and transient fetal hypoxia. The most appropriate next step is to initiate intrauterine resuscitation to maximize placental perfusion and oxygen delivery to the fetus. Standard resuscitative measures include maternal repositioning (typically to the left lateral decubitus position to relieve aortocaval compression), discontinuation of uterotonic agents such as oxytocin, administration of an intravenous fluid bolus, and providing supplemental oxygen. Proceeding directly to operative delivery is not indicated unless these measures fail or if the tracing deteriorates (e.g., absent variability).

Step-by-Step Solution

Analyze the fetal heart rate tracing described in the vignette.

The tracing shows symmetric decreases beginning after the contraction peak and returning to baseline after the contraction ends. These are late decelerations.

Accurate interpretation of fetal heart rate patterns is necessary to identify the underlying pathophysiology (in this case, uteroplacental insufficiency).

Determine the appropriate management for recurrent late decelerations.

The initial management involves intrauterine resuscitation to improve uteroplacental blood flow.

Interventions such as maternal repositioning (left lateral decubitus), stopping uterotonics (oxytocin), administering IV fluid boluses, and providing oxygen can correct transient hypoxia before resorting to operative delivery.

Evaluate the maternal vital signs and laboratory findings to rule out confounding complications.

The mild leukocytosis (

14,500/\text{mm}^3

) and mild anemia (

10.8\text{ g/dL}

) are noted to be normal physiologic changes of pregnancy.

This confirms that there is no indication for antibiotics or other interventions targeting a non-existent infection.

Key Concept

Recurrent late decelerations indicate uteroplacental insufficiency and should initially be managed with intrauterine resuscitation, including maternal repositioning and discontinuation of oxytocin.

Estimated Time:1m 30s

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