Enhanced FHR monitoring: No magic bullet

December 1, 2015

A recent trial reveals that ST-segment analysis does not improve CP rates.

 

Dr Lockwood, Editor-in-Chief, is Senior Vice President, USF Health, and Dean, Morsani College of Medicine, University of South Florida, Tampa. He can be reached at drlockwood@advanstar.com

 

Over the past 35 years, the rate of emergency cesarean deliveries has more than doubled while the prevalence of live births with cerebral palsy (CP) has remained nearly constant at around 2 per 1000 live births.1 Many view this as a major failure of continuous intrapartum electronic fetal heart rate (FHR) monitoring. Indeed, a 2013 meta-analysis of controlled trials of electronic FHR monitoring versus intermittent auscultation showed that the former yielded no significant improvement in overall perinatal death or CP rates but was associated with a significant increase in caesarean deliveries (RR 1.63, 95% CI 1.29–2.07, N = 18,861, 11 trials).2

Also read: ACOG Guidelines at a Glance: Antepartum fetal surveillance 

For a while, it was hypothesized that FHR monitoring coupled with fetal pulse oximetry produced more accurate diagnoses with fewer cesarean deliveries, but randomized controlled trials showed no such benefit.3 The search for a “magic bullet” to enhance the diagnostic precision of FHR monitoring resumed and initial studies from Europe suggested that sophisticated computerized detection of fetal academic-associated electrocardiographic ST segment elevation and increased T-wave amplitude might be the solution. Unfortunately, a recent carefully conducted randomized control trial has once again dashed our hopes for a better fetal intrapartum surveillance method.

A randomized trial of fetal ST segment analysis

The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units Network undertook a multicenter randomized trial in laboring women with singleton pregnancies at > 36 weeks’ gestation and cervical dilation of 2 to 7 cm.4 A total of 11,108 patients were randomly assigned to either "open" or "masked" monitoring with fetal ST segment analysis. In the latter group only routine FHR monitor data were available to clinicians, whereas in the former group, additional ST segment data were available when concerning FHR patterns were detected. Exclusion criteria included frankly nonreassuring FHR patterns prior to randomization and maternal or fetal conditions precluding a trial of labor or placement of a scalp electrode.

Study personnel were subject to pretrial training and a pilot phase to ensure competency with ST monitoring and uniformity of FHR pattern interpretation. The primary outcome was a composite of intrapartum fetal or neonatal death, Apgar score of ≤3 at 5 minutes, neonatal seizure, an umbilical-artery pH ≤7.05 or base deficit of ≥12 mmol/L, neonatal intubation, and encephalopathy. Secondary maternal outcomes included cesarean or operative vaginal delivery, chorioamnionitis, transfusion, and labor duration. Secondary neonatal outcomes included individual components of the composite score, Apgar score at 5 minutes, cord gas results, and admission to an intermediate or intensive care unit. The study was powered to detect a 40% reduction in the primary endpoint or a 25% reduction in cesarean delivery for nonreassuring FHR patterns.

Related: Legal: Failure to timely inform physician of changes on FHR strip 

 

 

Among the 5532 patients assigned to the open group and 5576 to the masked group, no differences were noted in the primary outcome (0.9% vs 0.7%, respectively; RR 1.31; 95% CI: 0.87–.98; P=0.20). In fact, the frequency of low 5-minute Apgar scores was significantly greater in neonates in the open versus masked group (0.3% vs 0.1%, P=0.02). No differences were noted in the prevalence of neonatal death or seizure, acidemia, intubation, intensive/intermediate care admission or neonatal encephalopathy. There were also no statistically or clinically significant differences in the rate of cesarean delivery (16.9% and 16.2%, respectively; P=0.30) or in the percent of cesareans for fetal indications (30.7% vs 33.1%, respectively). Operative deliveries also occurred with the same frequency (5.9% and 5.8%, respectively; P=0.31). No differences were noted in the occurrence of shoulder dystocia, chorioamnionitis, transfusion, or deliveries with dystocia. Even after adjusting for cases not managed according to protocol, no differences in outcomes were noted.

The authors concluded that use of ST segment analysis as an adjunct to continuous intrapartum FHR monitoring neither improved neonatal outcomes nor reduced cesarean delivery rates. These results are concordant with a number of other randomized trials. Vayssière and colleagues found no differences in cesarean or operative vaginal delivery rates with ST segment analysis but did note that fewer scalp pH studies were performed in the ST segment analysis group.5 Similar findings were noted by Ojala and associates.6 Schuit et al conducted an individual patient data meta-analysis using data from 4 randomized trials and observed no differences in neonatal metabolic acidosis or cesarean deliveries between the groups, although again, ST segment analysis did modestly reduce the frequency of fetal scalp samples (RR, 0.49; 95% CI, 0.44–0.55) and admissions to a neonatal intensive care unit among pregnancies >41 weeks (RR, 0.61; 95% CI, 0.39–0.95).7 However, because scalp pH assessments have fallen out of favor in the United States and because most American women are delivered before 42 weeks’ gestation, it is unclear what value such attributes would add to our current practices.

Where does this leave us?

Before you throw away the fetal monitors on your Labor and Delivery floor, it is important to note that while electronic FHR monitoring may be no better than intermittent auscultation, the latter is very labor-intensive for providers and subject to significant clinical variation in actual practice. Furthermore, no one will ever do a randomized clinical trial of FHR monitoring versus no monitoring, for the same reasons no one will ever do a randomized trial of parachutes versus no parachutes for skydivers.8

 

 

So why doesn’t FHR monitoring prevent CP? First, it is clear that at least a third of CP cases result from inflammation and/or prematurity.1 Furthermore, a considerable number of term infants with CP have genetic abnormalities (eg, trisomies, microdeletion syndromes, single-gene defects), epigenetic abnormalities, or unexplained developmental abnormalities often associated with malformations of the central nervous syndrome (CNS). Next, add perinatal strokes and placental vasculopathies causing prenatal degenerative CNS defects. Indeed, rates of congenital anomalies are far more common with the 2 antecedent obstetrical conditions most closely linked to CP: fetal growth restriction and preterm birth. Even fetal asphyxia, the one potentially preventable intrapartum etiology and the source of enrichment for so many trial lawyers, is accompanied by major malformations in 35% of cases.9 Moreover, many affected fetuses present to Labor and Delivery long after irreversible CNS damage has occurred. No wonder FHR monitoring has not meaningfully affected the occurrence of CP.

Take-home message

In the near term, it is unlikely that there will be any substitute for common sense and meticulous use of evidenced-based, uniform criteria when interpreting intrapartum FHR monitoring patterns to manage laboring patients. Moreover, such an approach should minimize but not eliminate unnecessary cesarean deliveries while maintaining a low incidence of intrapartum death, but it is not a magic bullet for prevention of CP.

References

1. Nelson KB, Blair E. Prenatal factors in singletons with cerebral palsy born at or near term. N Engl J Med. 2015;373(10):946–953.

2. Alfirevic Z, Devane D, Gyte GM. Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour. Cochrane Database Syst Rev. 2013;5:CD006066. Review.

3. East CE, Begg L, Colditz PB, Lau R. Fetal pulse oximetry for fetal assessment in labour. Cochrane Database Syst Rev. 2014;10:CD004075.

4. Belfort MA, Saade GR, Thom E, et al; Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. A Randomized Trial of Intrapartum Fetal ECG ST-Segment Analysis. N Engl J Med. 2015;373(7):632–641.

5. Vayssière C, David E, Meyer N, et al. A French randomized controlled trial of ST-segment analysis in a population with abnormal cardiotocograms during labor. Am J Obstet Gynecol. 2007;197(3):299.e1–6.

6. Ojala K, Vääräsmäki M, Mäkikallio K, Valkama M, Tekay A. A comparison of intrapartum automated fetal electrocardiography and conventional cardiotocography-a randomised controlled study. BJOG. 2006;113(4):419–423.

7. Schuit E, Amer-Wahlin I, Ojala K, et al. Effectiveness of electronic fetal monitoring with additional ST analysis in vertex singleton pregnancies at >36 weeks of gestation: an individual participant data meta-analysis. Am J Obstet Gynecol. 2013;208(3):187.e1-187.e13.

8. Smith GC, Pell JP. Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials. BMJ. 2003;327(7429):1459–1461. Review.

9. Nelson KB, Ellenberg JH. Antecedents of cerebral palsy. Multivariate analysis of risk. N Engl J Med. 1986;315(2):81–86.