Continuous External Fetal Heart Rate Monitoring During Labor

A 37-year-old pregnant woman at 39 weeks and 2 days' estimated gestation is admitted to the labor and delivery department with spontaneous rupture of membranes and active labor. Her pregnancy has been uncomplicated. She is negative for group B streptococci and has O+ blood type. All other laboratory test results are normal. She has had two prior pregnancies, both with uncomplicated vaginal deliveries.

On admission, she has clear amniotic fluid, and the fetus is in cephalic presentation. Her cervix is 6-cm dilated, and she is having painful contractions. Her initial blood pressure is 142/78 mm Hg; repeat blood pressure measurement 15 minutes later is 124/72 mm Hg. She has no history of gestational or chronic hypertension. She reports no headache, visual changes, or right upper quadrant abdominal pain. Results of a nonstress test on admission show a baseline fetal heart rate of 125 beats/min, with moderate variability, three accelerations in 20 minutes, no decelerations, and uterine contractions every 3 minutes. Automatic cycling upper extremity blood pressure measurement and continuous external fetal monitoring are initiated. She asks if she can remove the monitors to shower for adjunctive pain relief.

Continuous external fetal monitoring was introduced ostensibly to reduce perinatal mortality and the incidence of cerebral palsy. However, despite widespread use as standard of care, it has not been shown to alter those outcomes in low-risk laboring patients. American College of Obstetricians and Gynecologists guidelines generally define low-risk patients as those without meconium-stained fluid, abnormal intrapartum bleeding, abnormal or undetermined fetal test results, known or suspected congenital anomalies, intrauterine growth restriction, prior cesarean delivery, gestational or chronic diabetes or hypertension, or need for oxytocin induction or augmentation.¹

A Cochrane review showed that compared with intermittent auscultation, continuous external fetal monitoring increased risk of cesarean delivery and instrumental vaginal delivery but did not decrease the incidence of cerebral palsy or perinatal mortality. There was no difference in cord blood acidosis, hypoxic-ischemic encephalopathy, Apgar scores, or admission to the neonatal intensive care unit. Continuous external fetal monitoring decreased newborn seizure risk by one-half, although it remained a low-incident event. The number needed to treat (NNT) with continuous external fetal monitoring to prevent one seizure was 667, whereas that same number would cause 15 additional cesarean deliveries.²

Although historical studies of high-risk pregnancies were also not conclusive in supporting continuous external fetal monitoring,³ current evidence of its effects on low- vs high-risk pregnancies is lacking. It is important to note that most studies of continuous external fetal monitoring are more than 20 years old.²

A 2021 meta-analysis that included 33 trials and 118,863 patients showed that when compared with continuous external fetal monitoring, intermittent auscultation significantly reduced the risk of cesarean deliveries (risk ratio [RR] = 0.57–0.83) and instrumental vaginal deliveries (RR = 0.82). The NNT to avoid one cesarean delivery ranged from 2 to 6. The NNT to reduce one instrumental delivery was 6. There was no difference in neonatal acidemia, neonatal intensive care unit admissions, Apgar scores, or perinatal mortality. Fetal scalp blood pH sampling and fetal pulse oximetry monitoring did not improve outcomes.⁴