Fetal heart rate monitoring and the cesarean delivery rate

In this series, we have reviewed standard electronic fetal monitoring (EFM) nomenclature, challenged common notions about fetal heart rate (FHR) decelerations, and exposed a specious theory concerning intrapartum fetal head compression. This month's article will examine the evidence underlying the common perception that EFM increases the cesarean delivery rate.

History

When EFM replaced the traditional practice of intermittent auscultation in the 1970s, a series of studies reported significantly lower perinatal mortality rates in electronically monitored patients.^1-11 These studies were nonrandomized, and employed nonconcurrent controls, leading some to cite unrelated and simultaneous improvements in neonatal care and falling perinatal mortality rates as possible sources of bias.

Randomized controlled trials of EFM versus auscultation

In 1976, Haverkamp and colleagues reported the first prospective randomized study of 483 high-risk obstetric patients, comparing EFM with intermittent FHR auscultation in labor.¹³ There were no significant differences in perinatal mortality, Apgar scores, cord blood pH values, or neonatal morbidity between the EFM and control groups. The monitored group, however, had a significantly higher rate of cesarean delivery compared with the auscultated group (16.5% vs 6.6%, respectively).

A second study by Renou and colleagues in 1976 randomized 350 high-risk patients to EFM or intermittent auscultation during labor.¹⁴ There were no significant differences between the groups with respect to perinatal mortality, Apgar scores, or maternal or neonatal infection. Patients in the monitored group, however, had significantly higher umbilical cord blood pH values, significantly lower rates of admission to the neonatal intensive care unit (NICU), fewer neonatal neurologic signs or symptoms, and fewer cases of neonatal brain damage (not further defined). The cesarean delivery rate was again significantly higher in the monitored group than in the control group (22.3% vs 13.7%, respectively).

In 1978, Kelso and associates published a randomized controlled trial comparing EFM with intermittent auscultation in 504 low-risk patients.¹⁵ There were no significant differences between the groups with respect to perinatal mortality, low Apgar scores, cord blood pH values, NICU admissions or lengths of stay, neonatal or maternal infections, or abnormal neonatal neurologic findings. The only significant difference between the groups was an increase in incidence of cesarean birth in monitored patients compared with auscultated patients (9.5% vs 4.4%, respectively).

In 1979, Haverkamp and colleagues published another randomized controlled trial in high-risk patients. The design was similar to their first study, but additional measures of infant status were included as well as the option to perform fetal scalp pH determination during labor.¹⁶ A total of 690 high-risk patients were randomized into 3 groups. In the first group, fetal assessment during labor was accomplished by intermittent auscultation. The second group had continuous EFM alone, and the third group had continuous EFM with the option to measure scalp blood pH as needed. Among the 3 groups, no significant differences were seen in perinatal mortality, Apgar scores, cord blood pH values, maternal or neonatal infectious morbidity, NICU admissions, or neonatal neurologic abnormalities. A significantly increased incidence of cesarean birth was demonstrated in the group with EFM alone (18%) compared with auscultation alone (6%). The option to perform scalp blood sampling resulted in an intermediate cesarean delivery rate (11%) that was not significantly different from either of the other groups.