Evaluating Uterine Contractions and Fetal Heart Tracings in Third Trimester Pregnancy

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In Episode 61 of Med School Question of the Week for USMLE, Faustine Ramirez, MedSchoolCoach expert tutor, answers this medical school question: A 25-year-old primigravid woman at 39 weeks’ gestation is admitted to the hospital in labor. She had spontaneous rupture of membranes 24 hours ago. She reports good fetal movement and regular, painful uterine contractions. Temperature is 38.6 C, heart rate is 116/min, respiratory rate is 22/min, and blood pressure is 98/67. Respirations are mildly labored and lungs are clear to auscultation bilaterally. There is pronounced tenderness to palpation over the uterine fundus. No costovertebral angle tenderness is noted. The cervix is 4 cm dilated and 70% effaced, and the vertex is at -2 station. Laboratory studies reveal a serum leukocyte count of 18,500 with a left shift. Microscopic examination of a clean catch urine specimen shows no leukocytes or bacteria. A fetal heart tracing is shown in the video. Which of the following is the most likely cause of this fetal heart tracing?