February 11, 2025

A 24-year-old G2P1 presents to labor and delivery in latent labor at 37 weeks

By Med-Challenger · 1 minute read

A 24-year-old G2P1 presents to labor and delivery in latent labor at 37 weeks. Her contractions are every 5-6 minutes, and her cervix is 2 cm/80% effaced/-1 station. She is Group B Strep positive and is receiving penicillin IV for prophylaxis.

Her pregnancy has been complicated by gestational hypertension, and her blood pressure at admission is 140/90 mm Hg. Fetal heart rate (FHR) tracing initially shows a baseline of 140 bpm with moderate variability and accelerations. No decelerations are noted.

She requests medication for pain relief and is given morphine 10 mg IV x 1 dose. Shortly thereafter, the FHR tracing shows decreased variability and very few accelerations.

Which of the following is most likely responsible for the change in FHR tracing?

Group B Strep positive
IV morphine
gestational hypertension
IV penicillin
37 weeks’ gestational age

The correct answer is:

IV morphine

The most likely cause of the decreased variability and decreased number of fetal heart rate (FHR) accelerations is IV morphine. At equivalent doses, all narcotics (with or without added antiemetics) similarly cause a decrease in variability and a decrease in the frequency of accelerations. Penicillin, hypertension, and the presence of Group B Strep should have no effect on the fetal heart rate tracing. While abnormal FHR tracings can occur in up to 60% of women with preterm labor, the fetus in this case is 37 weeks and should not have an abnormal FHR tracing related solely to gestational age.

References:

Intrapartum Fetal Heart Rate Monitoring: Nomenclature, Interpretation, and General Management Principles. ACOG Practice Bulletin: Clinical Management Guidelines for Obstetrician-Gynecologists. Number 106, July 2009.

Young BK. Intrapartum fetal heart rate assessment. UpToDate. Updated October 17, 2011.

This question appears in Med-Challenger OBGYN Exam Review with CME

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