Review Question - QID 108729

A 35-year-old G2P1001 at 38 weeks of gestation presents to the obstetric triage unit with 3 hours of periodic contractions. She reports that she felt a gush of clear fluid followed by a small amount of blood about 20 minutes ago. On her way to the hospital, the contractions have become stronger and more frequent. The fetus has remained active throughout this time period. The patient has a history of chronic hypertension that has been stable during this pregnancy. She had a spontaneous vaginal delivery 2 years ago and is also a carrier of the sickle cell trait, as is her husband. They declined to have genetic testing of their child and a recent growth ultrasound showed a fetus at the 76th percentile. Upon admission to the labor floor, the patient’s temperature is 98.4°F (36.9°C), blood pressure is 121/82 mmHg, pulse is 80/min, and respirations are 14/min. Ultrasound reveals a cephalic presenting fetus and speculum exam shows a pool of clear fluid in the vaginal vault. The cervix is 7 centimeters dilated and 90% effaced. The fetus is at -1 station. The patient receives an epidural and an intrapartum fetal heart rate tracing is shown in Figure A. Which of the following is the most likely underlying physiology of this tracing?