A 34-year-old woman comes to the labor and delivery unit via ambulance for contractions, rupture of membranes, and vaginal bleeding. The patient had rupture of membranes 4 hours ago, and her contractions have increased in intensity and frequency over the last hour, which required multiple doses of morphine in the ambulance. On arrival, temperature is 37.2 C (99 F), blood pressure is 130/80 mm Hg, and pulse is 94/min. On pelvic examination, the membranes are grossly ruptured with clear fluid, and there is scant, dark blood on the perineum. The cervix is 6 cm dilated and 80% effaced, and fetal position is occiput posterior. Fetal heart rate tracing is shown in the exhibit. Which of the following is the most likely cause of this fetal heart rate tracing?

Question

A 34-year-old woman comes to the labor and delivery unit via ambulance for contractions, rupture of membranes, and vaginal bleeding.  The patient had rupture of membranes 4 hours ago, and her contractions have increased in intensity and frequency over the last hour, which required multiple doses of morphine in the ambulance.  On arrival, temperature is 37.2 C (99 F), blood pressure is 130/80 mm Hg, and pulse is 94/min.  On pelvic examination, the membranes are grossly ruptured with clear fluid, and there is scant, dark blood on the perineum.  The cervix is 6 cm dilated and 80% effaced, and fetal position is occiput posterior.  Fetal heart rate tracing is shown in the exhibit.  Which of the following is the most likely cause of this fetal heart rate tracing?

Quizplus · Accepted Answer

11ec25c8_da31_dba8_bc81_df22a8f5c845_MD0003_00 During labor, fetal heart rate monitoring is performed to continuously assess for signs of fetal hypoxia and metabolic acidosis, which can lead to fetal compromise. Fetal heart rate features that are monitored include the baseline heart rate (normal: 120-160/min), presence of accelerations and/or decelerations, and heart rate variability. Variability is the beat-to-beat fluctuation in baseline fetal heart rate. These fluctuations are irregular in amplitude and frequency and categorized based on amplitude change (measured from peak to trough). Normal variability, a change in baseline of 6-25/min, is reassuring. In contrast, persistently absent or minimal variability (ie, ?5/min), as in this patient, can indicate fetal metabolic acidosis and impending fetal compromise. this patient However, certain medications can cause transient absent or minimal variability unrelated to fetal acid-base status. Opioids (eg, morphine) may decrease fetal heart rate variability due to fetal CNS depression; exposed fetuses also typically have decreased frequency of accelerations. These changes are temporary and normalize as the medication effect diminishes; therefore, these patients typically require only continued monitoring. (Choice A) A congenital cardiac anomaly may cause tachypnea and cyanosis in the newborn but does not typically change fetal heart rate variability in utero because fetal oxygenation is via the placenta. (Choice B) The fetal occiput posterior position can increase the rate of early decelerations due to greater fetal head compression; however, it does not cause decreased variability. occiput posterior position early decelerations (Choice C) An intraamniotic infection can cause minimal variability due to infection-induced fetal hypoxia; however, patients typically have maternal fever, causing fetal tachycardia (baseline: >160/min). This patient is afebrile and has a normal fetal baseline, making this diagnosis unlikely. fetal tachycardia (Choice E) Uteroplacental insufficiency, or inadequate blood flow to the placenta and fetus, may produce fetal hypoxia, acidosis, and resultant minimal variability. However, patients typically also have late decelerations. This patient has no decelerations or risk factors for uteroplacental insufficiency (eg, preeclampsia). late decelerations Educational objective: Persistently absent or minimal variability on fetal heart rate monitoring typically indicates fetal metabolic acidosis. However, certain medications (eg, opioids) can also cause decreased variability (eg, fetal CNS depression). References: Variations on fetal heart rate variability. (http://www.ncbi.nlm.nih.gov/pubmed/26926317) Practice bulletin no. 116: management of intrapartum fetal heart rate tracings. (http://www.ncbi.nlm.nih.gov/pubmed/20966730)

A 34-Year-Old Woman Comes to the Labor and Delivery Unit