ST analysis of the fetal electrocardiogram during labor: Nordic observational multicenter study

Objective: To assess the diagnostic power of cardiotocography (CTG) plus the ST interval of the electrocardiogram (ECG) clinical guidelines with combined fetal heart rate and ST waveform analysis of the fetal ECG recorded during labor, to identify an adverse labor outcome (neonatal neurological symptoms and/or metabolic acidosis). Study design: An observational, multicenter study was undertaken in 12 Nordic labor wards. A total of 573 women in labor were monitored using a prototype of the STAN® S 21 recorder with fetal ECG data and computerized ST analysis. Results: Fifteen cases of intrapartum fetal hypoxia identified from neurological neonatal symptoms and/or cord artery pH < 7.05 with base deficit in extracellular fluid > 12.0 mmol/l were recorded. All these cases were identified by CTG + ST clinical guidelines. Five developed neonatal symptoms and had ECG abnormalities during the first stage of labor and, of the remaining ten, eight showed ST changes during active pushing in the second stage. Another eight cases had acidemia only and normal neonatal outcome. Seven of these displayed CTG + ST abnormalities. The high sensitivity of CTG + ST to predict fetal acidosis was associated with a marked increase in positive predictive values compared with conventional CTG. Conclusion: The STAN clinical guidelines identify fetuses at risk of intrapartum asphyxia.     

ST Waveform Analysis versus Cardiotocography Alone for Intrapartum Fetal Monitoring: A Meta-Analysis of Randomized Trials

Objective To estimate the effectiveness of intrapartum ST waveform analysis (STAN) versus cardiotocography (CTG) alone in prevention of metabolic acidosis.Study Design Meta-analysis of randomized trials comparing intrapartum fetal monitoring utilizing STAN with CTG versus CTG alone. Primary outcome was neonatal metabolic acidosis, defined as umbilical arterial pH <7.05 and base deficit >12 mmol/L.Results Five randomized trials including 15,303 singletons, vertex, term, or near-term pregnancies met inclusion criteria and were analyzed. Compared with CTG alone, STAN with CTG was associated with similar incidences of metabolic acidosis (0.81% versus 1.12%, relative risk [RR] 0.80; 95% confidence interval [CI] 0.44 to 1.47), perinatal death, neonatal encephalopathy, Apgar score <7 at 5 minutes, admission to neonatal intensive care unit, and cesarean delivery. Operative vaginal delivery (OVD) was lower in the STAN with CTG compared with CTG alone (13.56% versus 15.20%; RR 0.89; 95% CI 0.83 to 0.97).Conclusion There is no difference in perinatal outcomes between STAN with CTG compared with CTG alone, except for lower rate of OVD.     

A comparison of intrapartum automated fetal electrocardiography and conventional cardiotocography--a randomised controlled study

Objective  To examine whether intrapartum monitoring by means of automatic ST analysis (STAN) of fetal electrocardiography could reduce the rate of neonatal acidemia and the rate of operative intervention during labour, compared with monitoring by means of cardiotocography (CTG).
Design  Randomised controlled trial.
Setting  Labour ward in tertiary-level university hospital.
Sample  A total of 1483 women in active labour with singleton term fetus in cephalic presentation.
Methods  Women were randomly assigned to be monitored either by STAN or by CTG. Fetal blood sampling (FBS) was optional in both groups.
Main outcome measures  Neonatal acidemia (umbilical artery pH <7.10), neonatal metabolic acidosis (umbilical artery pH <7.05 and base excess <−12 mmol/l) and operative interventions: caesarean section rate, vacuum outlet (VO) rate and FBS rate.
Results  There were no statistically significant differences between the STAN group and CTG group in the incidence of neonatal acidemia (5.8 versus 4.7%) or metabolic acidosis (1.7 versus 0.7%). The caesarean section rate (6.4 versus 4.7%) and the VO rate (9.5 versus 10.7%) were also similar in the STAN and CTG groups. The incidence of FBS was lower ( P < 0.001) in the STAN group (7.0%) than in the CTG group (15.6%).
Conclusions  Intrapartum fetal monitoring by means of automatic STAN did not improve the neonatal outcome or decrease the caesarean section rate. However, the need for FBS during labour was lower in the STAN group.     

Fetal pulse oximetry and wavelet analysis of the fetal heart rate in the evaluation of abnormal cardiotocography tracings

AIM: Previous studies indicate that the addition of wavelet analysis of the fetal pulse oximetry tracings (FSPO2) and fetal heart rate (FHR) variability to cardiotocography (CTG), for intrapartum fetal monitoring, provides useful information on the fetal response to hypoxia. We applied the new procedure in non-reassuring CTG patterns, in which cesarean section was performed, and tested its accuracy in the diagnosis of the intrapartum fetal compromise. METHODS: At the 'Aretaieion' University Hospital labor ward, 318 women with term fetuses in the cephalic presentation entered the trial during labor. They all were monitored with external CTG and fetal pulse oximetry. In the cases that cesarean section was applied, because of abnormal CTG tracings, we applied a method based on the multiresolution wavelet analysis and a self-organized map neural network on the first and second stage of labor. The main outcome parameter was the rate of cord metabolic acidosis at birth (pH < 7.05). Secondary outcomes included Apgar scores at 5 min, fetal transmission to neonatal intensive care unit (NICU) and neonatal encephalopathy. RESULTS: Fifty out of 318 cases delivered operatively because of abnormal CTG patterns (rate 15.72%). In 30 cases, cord pH was >7.05, while in 11 Apgar scores at 5 min were <7, while none of those neonates were transferred to NICU. In the rest 20 cases cord pH was <7.05; in all of these cases Apgar scores at 5 min were <7, while four neonates were transferred to NICU. In one of them, neonatal encephalopathy was diagnosed. After the offline application of wavelet analysis and neural networks to the pulse oximetry and FHR variability readings of the 50 cases, statistics calculated that the system showed a sensitivity of 85% and a specificity of 93%, while false negative and false positive rates were 15% and 7%, respectively. CONCLUSION: Computerized FHR and FSPO2 monitoring shows an excellent efficacy and reliability in interpreting non-reassuring FHR recordings.     

How deviations from STAN guidelines contribute to operative delivery for suspected fetal distress

Objective

To evaluate how deviations from STAN guidelines contribute to operative delivery for suspected fetal distress in a high-risk population.

Study design

This retrospective cohort study was conducted in a tertiary referral center with about 3000 deliveries a year. During the study period, STAN usage rate was 15.2%. All consecutive patients monitored with STAN who had an operative delivery for suspected fetal distress were included in the index group. Patients who delivered spontaneously or had an operative delivery for any reason other than suspected fetal distress were included as controls. Case review was performed by three referent obstetricians for STAN technology blinded to neonatal outcomes. Main outcome was agreement between decision made and decision recommended by STAN clinical guidelines. Secondary outcomes were reasons explaining guideline deviation and ST event to birth interval in cases with a significant ST event.

Results

Eighty-three patients were included in each group. Decision made was consistent with STAN clinical guidelines in 124 patients (74.7%): 50 patients (60.2%) in the index group and 74 patients (89.2%) in the control group (p < 0.05). Among these patients, no fetal metabolic acidosis was reported. Decision made was not consistent with STAN labor management guidelines in 42 patients (24.3%): 33 patients (39.8%) in the index group and 9 (10.8%) in the control group (p < 0.05). Including ST event to birth interval, interventions were outwith STAN clinical guidelines in 51.4% of patients with suspected fetal distress. CTG misclassification was involved in over 75% of cases.

Conclusion

STAN guideline deviations contribute to an increased operative delivery rate in patients with suspected fetal distress and normal neonatal outcomes. Guideline deviations are more frequent in patients with suspected fetal distress than in controls. CTG misclassification was the leading cause of guideline deviation. STAN guideline deviations may contribute to alter STAN specificity.     

STAN S21 fetal heart monitor for fetal surveillance during labor: an observational study in 637 patients.

OBJECTIVE: To assess the value of the STAN fetal heart monitor for intrapartum fetal monitoring using cardiotocography (CTG) and fetal electrocardiography (ECG). DESIGN: Prospective observational study. MATERIAL AND METHODS: Between August 2000 and November 2002, 637 high-risk labors were monitored using a STAN S21 fetal heart monitor, providing CTG plus automatic ST analysis of the fetal ECG. Guidelines with recommendations about when to intervene were available. During the study period labor-ward personnel were systematically instructed about the (patho)-physiology of asphyxia and CTG and ST changes during labor. RESULTS: Four hundred and forty-nine recordings were available for analysis of outcome in relation to ST changes. In 61 cases, ST changes requiring intervention occurred > 10 min before birth. In 35 (57%) of these cases, umbilical artery blood pH at delivery was < 7.15. Eighteen (4.0%) neonates were born with metabolic acidosis (umbilical artery pH < 7.05 and extracellular base deficit > 12 mmol/l). Significant ST changes (18-31 min before birth) were present in all five cases with pH < 7.00 and in six of the 13 cases with pH of 7.00-7.04 (false-negative rate 1.6%). Neonatal follow-up showed no adverse outcome. One hundred and ninety-two fetal blood samples (121 in the first stage and 71 in the second stage of labor) were taken from 142 women. Fetal scalp blood pH was < 7.15 in ten samples, 7.15-7.19 in 11 samples, 7.20-7.24 in 30 samples and > or =7.25 in 141 samples. ST changes occurred in eight (80%), six (55%), nine (30%) and 15 (11%) of these cases, respectively. In 188 (29.5%) women, outcome could not be analyzed in relation to ST changes because of inadequate recording (time between end of recording and delivery > 20 min or poor signal quality) or the absence of umbilical cord gases. In this group, four (2.1%) neonates with metabolic acidosis were born. In three of these cases the fetal ECG signal was of was poor quality and in one case the recording had ended 60 min before birth. CONCLUSION: ST changes were present in all five cases with severe metabolic acidosis (umbilical artery pH < 7.00). ST changes occurred in 46% of cases with mild metabolic acidosis. CTG plus ST analysis was more specific in detecting fetal acidemia than CTG alone.     

Fetal scalp pH and ST analysis of the fetal ECG as an adjunct to cardiotocography to predict fetal acidosis in labor--a multi-center, case controlled study

OBJECTIVE: To assess the relationship between scalp pH (FBS) and ST analysis in situations of acidosis with special emphasis on the timing of cardiotocography (CTG), FBS and ST changes during labor. STUDY DESIGN: From a European Union multicenter study on clinical implementation of the STAN methodology, 911 cases were identified where a scalp-pH had been obtained. In 53 cases, marked cord artery acidosis was found (cord artery pH<7.06) and 44 cases showed moderate acidemia at birth (pH 7.06-7.09). Comparisons were made with 97 control cases (pH>or=7.20). RESULTS: Of those cases with FHR+ST events recorded within 16 min of delivery, 61% (17/28) had a cord artery pH>or=7.20. The corresponding figure for cases where STAN indications occurred for more than 16 min was 19% (13/69) (OR 6.66, 2.53-17.55, P<0.001). Out of the 121 cases with an abnormal CTG, 84 (69%) showed a cord artery pH of <7.10. STAN indicated abnormality in 83% (70 out of 84). The corresponding figure for scalp pH<7.20 was 43% (36/84). In the case of CTG changes at the start of an adequate recording STAN guidelines provided information on developing acidosis in all cases but one (16 out of 17) in the marked acidosis group. STAN guidelines indicated abnormality prior to an abnormal FBS in 14 out of 17 cases. The median duration between STAN indications to intervention and an abnormal FBS was 29 (95% CI 11-74) min. CONCLUSIONS: ST analysis, as an adjunct to CTG, identifies adverse fetal conditions during labor similar to that of FBS but on a more consistent basis. The timing of CTG+ST changes relates to the level of acidosis at birth.     

Fetal electrocardiotocography in labor and neonatal outcome: an observational study in 1889 patients in the French center of Edouard Herriot, Lyon.

BACKGROUND: The STAN methodology has been shown to reduce both operative delivery for fetal distress and the cord artery metabolic acidosis rate. OBJECTIVE: The objective of this study was to monitor delivery modes and perinatal outcomes following the introduction of the STAN methodology and the evolution of its use at our institution. METHODS: Two periods were characterized: June 2000-June 2002 (period 1) and July 2002-April 2005 (period 2). Parity, mode of labor and delivery, ST events, and neonatal outcome (Apgar score and pH of the umbilical cord artery and vein), cases of metabolic acidosis and operative delivery for fetal distress were studied. RESULTS: One thousand eight hundred and eighty-nine women were included in the study. The rate of use of STAN increased from 13.5% to 16% over these two time periods. The rate of metabolic acidosis was low: 0.28% and 0.45%, respectively. No cases of neonatal encephalopathy or of perinatal death were diagnosed. There was a decrease in the rate of operative delivery for fetal distress (163/701 (22.9%) vs. 228/1111 (20.3%), p = 0.26). CONCLUSIONS: According to the literature, our use of the STAN appears to be very successful; the metabolic acidosis rate was 0.38% and the rate of operative delivery for fetal distress decreased. We improved the accuracy of the interpretation of the fetal heart rate.     

Fetal scalp pH and ST analysis of the fetal ECG as an adjunct to CTG. A multi-center, observational study

OBJECTIVE: To evaluate the relationships between scalp-pH and CTG plus ST waveform analysis of the fetal ECG (STAN) clinical guidelines as indicators of intrapartum hypoxia in term fetuses born with cord artery acidemia. STUDY DESIGN: Data from 6999 term deliveries monitored by the STAN (R) S 21 as part of an EU multi-center study on clinical implementation of the STAN methodology for intrapartum fetal surveillance were analyzed. We identified 911 cases where a scalp-pH was obtained, including 53 cases with cord artery acidemia (pH < 7.06). Lag times between ST events and scalp-pH and time to delivery were related to cord artery metabolic and respiratory acidosis and neonatal outcome. RESULTS: 43 fetuses were identified by CTG plus ST as being in need of intervention 31 (25-46) minutes before delivery (median, 95% Cl). In five, no indications were given and in another five there were inadequate data. Fifteen cases with metabolic acidosis required special neonatal care, all 14 cases adequately monitored on STAN had indications to intervene for 19 minutes or more. In 30 adequately recorded cases, fetal blood sampling (FBS) was obtained within the last hour of labor. In 22 cases, FBS was obtained 13 (7-24) minutes after STAN guidelines had indicated abnormality and in eight no ST changes had occurred at time of FBS. The corresponding FBS data were pH 7.10 (7.01-7.15) and pH 7.21 (7.08-7.31), respectively, P = 0.01. In cases of metabolic acidosis, scalp-pH fell 0.01 units per minute after a baseline T/QRS rise was recorded during the second stage of labor. Apart from one newborn that died at 2 h from E. Coli septicemia, none of the neonates were affected neurologically. CONCLUSION: Cardiotocography plus ST analysis provides accurate information about intrapartum hypoxia similar to that obtained by scalp-pH.     

Fetal electrocardiogram ST-segment analysis and prediction of neonatal acidosis.

OBJECTIVE: To determine the diagnostic value of fetal ST-segment analysis (STAN) in predicting neonatal acidosis. METHODS: The STAN S21 was used to monitor singleton fetuses in labor with abnormal FHR. Physicians later reviewed tracings to identify any ST events dictating intervention. Outcome measures were umbilical artery pH< or =7.15 and pH< or =7.05 at birth. The sensitivity, specificity, PPV, and NPV of a significant ST event to predict both outcomes were calculated. RESULTS: Analysis included 411 women. Sensitivity of a significant ST event for screening pH< or =7.15 (21.9%) was 38% (41/108), specificity 83% (252/303), PPV 45% (41/92) and NPV 79% (252/319), and for pH< or =7.05, it was (3.4%), 62.5% (10/16), 79% (313/395), 11% (10/92), and 98% (313/319), respectively. CONCLUSION: In a population with abnormal FHR in labor, STAN sensitivity is moderate (almost 40%) for predicting pH< or =7.15 and better (almost 60%) for more severe acidosis (pH< or =7.05).     

Assessment of STAN S21 fetal heart monitor by medical staff.

OBJECTIVE: To compare the responses of medical staff using the STAN S21 fetal heart monitor versus standard cardiotocography (CTG) to monitor abnormal fetal heart rate in labor. METHOD: Questionnaires were completed by medical staff involved in a randomized controlled trial to compare STAN surveillance with traditional surveillance before the trial had finished. Respondents were questioned about their experience and confidence using the STAN system. RESULTS: The response rate was 82% (89/109). Overall, 71% of respondents preferred using STAN surveillance, while 5% preferred standard CTG. Reasons given for preference over CTG alone were the continuous nature of surveillance (47%), the need for fewer scalp pH tests (39%), and its capacity to screen for severe fetal distress (30%). CONCLUSION: Most of the medical staff surveyed preferred using STAN versus standard surveillance techniques to monitor abnormal fetal heart rate during labor.     

Use of peripartum ST analysis of fetal electrocardiogram without blood sampling: a large prospective cohort study

Objective

Fetal peripartum surveillance with ST analysis of fetal electrocardiogram (STAN) alone or in combination with fetal blood sampling (FBS) is a worldwide debate. STAN monitoring without FBS support was implemented in 2000 in the authors’ department when it took part in a European multicentre project. The aim of this study was to evaluate neonatal outcomes associated with peripartum STAN monitoring without FBS support in a large prospective cohort of patients at high risk of peripartum fetal asphyxia.

Study design

This prospective cohort study included all consecutive high-risk women monitored with STAN technology over a 77-month period, excluding fetuses with congenital anomalies. Outcome variables were fetal metabolic acidosis, umbilical pH ≤ 7.05 and normal extracellular base deficit, transfer to a neonatal intensive care unit, neonatal encephalopathy and neonatal death related to peripartum asphyxia. Cases with metabolic acidosis were reviewed by a referent midwife and referent obstetricians to check whether or not labour management was consistent with the STAN guidelines.

Results

In total, 3112 women were included in the study. The caesarean section rate for suspected fetal distress was 9.5% [95% confidence interval (CI) 8.5-10.5]. Acid-base status was available for 3067 (98.5%) neonates. There were 14 cases of fetal metabolic acidosis (0.45%; 95% CI 0.2-0.7), 62 cases with umbilical pH ≤ 7.05 and normal extracellular base deficit (2%; 95% CI 1.5-2.5), 27 neonates with 5-min Apgar scores ≤ 7 (0.87%; 95% CI 0.54-1.20) and 16 neonates were transferred to the neonatal intensive care unit (0.51%; 95% CI 0.26-0.76) due to peripartum asphyxia. No cases of neonatal encephalopathy, or fetal or neonatal death occurred. Out of the 14 cases of fetal metabolic acidosis, 11 were not managed in accordance with the STAN guidelines. Specificity was 80.5% and the negative predictive value was 99.9%. Sensitivity was highly affected by medical staff interpretation, varying from 9.1% in the authors’ experience to 90.9% with appropriate labour management according to the STAN guidelines.

Conclusions

STAN monitoring without FBS support was associated with a low rate of fetal metabolic acidosis. Most cases of fetal metabolic acidosis were not managed in accordance with the STAN guidelines. This study not only supports STAN usage without FBS support, but also warns of possible guideline violations and subsequent adverse neonatal outcomes.     

Fetal ST segment heart rate analysis in labor: improvement of intervention criteria using interpolated base deficit.

OBJECTIVE: The addition of ST waveform analysis (STAN, Neoventa, Sweden) to fetal heart rate (FHR) tracings has been demonstrated to improve fetal outcome and reduce operative delivery rates, though the actual level of fetal acidosis at which STAN indicates intervention has not been assessed. We sought to determine if FHR ST segment analysis recommends intervention at appropriate levels of fetal acidosis. METHODS: FHR tracings of 10 acidotic and 10 non-acidotic infants with FHR tracings having a minimum of one STAN flag were retrospectively analyzed. Fetal base deficit (BD) was calculated by interpolation throughout the FHR tracing and STAN 'action' and 'ignore' flags assigned a fetal BD value. A secondary analysis was performed with a revised interpretation of FHR reassuring status. RESULTS: The mean (+/-SD) BD of the first STAN action was significantly greater than the first 'ignore' (4.0+/-2.1 vs. 3.0+/-0.8 mmol/L, p<0.05). Clarified STAN criteria for reassuring vs. non-reassuring FHR resulted in a first action BD of 6.0+/-2.0 mmol/L with 90% sensitivity and 100% specificity for prediction of fetal acidosis. CONCLUSION: The STAN monitor discriminates increasing levels of fetal BD. With clarification of the criteria for reassuring FHR, the calculated BDs of action flags are an appropriate threshold for emergent intervention, successfully predict acidotic fetuses, and avoid unnecessary intervention.     

Fetal electrocardiotocography in labor and neonatal outcome: An observational study in 1889 patients in the French center of Edouard Herriot,Lyon

Background. The STAN methodology has been shown to reduce both operative delivery for fetal distress and the cord artery metabolic acidosis rate.

Objective. The objective of this study was to monitor delivery modes and perinatal outcomes following the introduction of the STAN methodology and the evolution of its use at our institution.

Methods. Two periods were characterized: June 2000–June 2002 (period 1) and July 2002–April 2005 (period 2). Parity, mode of labor and delivery, ST events, and neonatal outcome (Apgar score and pH of the umbilical cord artery and vein), cases of metabolic acidosis and operative delivery for fetal distress were studied.

Results. One thousand eight hundred and eighty-nine women were included in the study. The rate of use of STAN increased from 13.5% to 16% over these two time periods. The rate of metabolic acidosis was low: 0.28% and 0.45%, respectively. No cases of neonatal encephalopathy or of perinatal death were diagnosed. There was a decrease in the rate of operative delivery for fetal distress (163/701 (22.9%) vs. 228/1111 (20.3%), p = 0.26).

Conclusions. According to the literature, our use of the STAN appears to be very successful; the metabolic acidosis rate was 0.38% and the rate of operative delivery for fetal distress decreased. We improved the accuracy of the interpretation of the fetal heart rate.     

Foetal ECG and STAN technology—a review

Waveform analysis of the foetal electrocardiogram (FECG) has been studied from physiological, signal processing and clinical aspects. Two randomised controlled trials (RCT) have been performed during the last 20 years, monitoring high-risk labours with cardiotocography (CTG) only or combining CTG with the ST waveform analysis of the FECG. A significant decrease in neonates born with metabolic acidosis in cord artery blood was observed, along with a decrease of operative deliveries for foetal distress. Blinded assessment of neonatal outcome in the latest RCT revealed an improvement of the Apgar score and the need for intensive care and neonatal encephalopathy when monitoring with CTG in combination with FECG. Also, the interobserver agreement for ST analysis was higher than for CTG alone. The system ability of the STAN technology, including an educational model, was studied in several European University clinics as an EU-supported project. During the last 6 months, the project confirmed the incidence of metabolic acidosis (0.64%) and moderate/severe encephalopathy in the earlier RCT on using ST information in addition to CTG. The available evidence suggests that the expected outcome could be achieved in most clinics, with a special focus on systematic teaching and training. Compared to ST analysis, foetal blood sampling (FBS) for pH analysis is technically complicated and, because it only presents momentary information, needs to be repeated to give adequate information. The STAN method provides continuous on-line information. ST waveform analysis in addition to CTG has the potential to give significant benefits in reducing operative deliveries for foetal distress and reducing the incidence of metabolic acidosis. However, this will depend on the appropriate education and use of STAN according to the guidelines provided.     

STAN, a clinical audit: the outcome of 2 years of regular use in the city of Varberg, Sweden

OBJECTIVE: To monitor and analyze (audit) the introduction of the STAN methodology in a district hospital. DESIGN: Retrospective study covering the total population of deliveries at term during 2004 and 2005. MATERIAL AND METHODS: 1,875 out of 3,193 term pregnancies (59%) were monitored using the STAN fetal heart monitor (Neoventa Medical, Moelndal, Sweden) and the associated clinical guidelines. Cord metabolic acidosis, neonatal outcome, and rates of operative deliveries for fetal distress were recorded. RESULTS: The overall cesarean section rate was significantly reduced in the STAN group. Emergency (crash) cesarean sections were significantly reduced from 1.51% to 0.27% in the cardiotocography- and STAN-monitored groups, respectively (OR 0.18, 95% CI 0.07-0.49). When cesarean section was performed only because of non-reassuring cardiotocography, cord acid base was significantly higher, 7.26 versus 7.19 (p<0.01), as compared to when STAN guidelines were followed. Total population rates for operative deliveries for fetal distress and cesarean section rates were 6.7% and 3.5% respectively. The corresponding metabolic acidosis rate was 0.5%. CONCLUSION: High STAN usage in a busy labor ward setting provided an outcome equaling that noted previously in a larger academic unit, demonstrating the safe implementation of the STAN methodology in a nonacademic unit.     

Review of the first 1502 cases of ECG-ST waveform analysis during labour in a teaching hospital

Objective  To assess the impact of introduction of the STAN monitoring system.
Study design  Prospective observational study.
Setting  Tertiary referral labour ward, St George's Hospital, London.
Population  High-risk term pregnancies.
Methods  We report all consecutive cases of intrapartum monitoring using the STAN S 21 fetal heart monitor. Cases with adverse neonatal outcome were evaluated in relation to the ST waveform analysis and cardiotocography (CTG).
Main outcome measures  Cord artery metabolic acidosis, neonatal encephalopathy (NNE) and reasons behind cases with poor outcome.
Results  Between 2002 and 2005, there were 1502 women monitored by STAN. Based on combined STAN analysis in the 1502 women, action was indicated in 358 women (23.8%), while in 1108 women (73.8%) no action was indicated. Traces were not interpretable in 36 women (2.4%). Of the 836 cases (55.7%) where cord blood gases were available, there were 23 cases (2.8%) of metabolic acidosis and 16 of these (70%) were identified by STAN. Overall, there were 14 cases of NNE monitored by STAN. Retrospective analysis of these highlights human errors, such as poor CTG interpretation, delay in taking appropriate action and not following the guidelines.
Conclusions  Our experience suggests the need for more intense training on interpretation of CTG and strict adherence to guidelines.     

STAN® S21 fetal heart monitor for fetal surveillance during labor: an observational study in 637 patients

Objective: To assess the value of the STAN^® fetal heart monitor for intrapartum fetal monitoring using cardiotocography (CTG) and fetal electrocardiography (ECG).

Design: Prospective observational study.

Material and methods: Between August 2000 and November 2002, 637 high-risk labors were monitored using a STAN^® S21 fetal heart monitor, providing CTG plus automatic ST analysis of the fetal ECG. Guidelines with recommendations about when to intervene were available. During the study period labor-ward personnel were systematically instructed about the (patho)-physiology of asphyxia and CTG and ST changes during labor.

Results: Four hundred and forty-nine recordings were available for analysis of outcome in relation to ST changes. In 61 cases, ST changes requiring intervention occurred >?10?min before birth. In 35 (57%) of these cases, umbilical artery blood pH at delivery was <?7.15. Eighteen (4.0%) neonates were born with metabolic acidosis (umbilical artery pH <?7.05 and extracellular base deficit >?12?mmol/l). Significant ST changes (18–31?min before birth) were present in all five cases with pH <?7.00 and in six of the 13 cases with pH of 7.00–7.04 (false-negative rate 1.6%). Neonatal follow-up showed no adverse outcome. One hundred and ninety-two fetal blood samples (121 in the first stage and 71 in the second stage of labor) were taken from 142 women. Fetal scalp blood pH was <?7.15 in ten samples, 7.15–7.19 in 11 samples, 7.20–7.24 in 30 samples and ??7.25 in 141 samples. ST changes occurred in eight (80%), six (55%), nine (30%) and 15 (11%) of these cases, respectively. In 188 (29.5%) women, outcome could not be analyzed in relation to ST changes because of inadequate recording (time between end of recording and delivery >?20?min or poor signal quality) or the absence of umbilical cord gases. In this group, four (2.1%) neonates with metabolic acidosis were born. In three of these cases the fetal ECG signal was of was poor quality and in one case the recording had ended 60?min before birth.

Conclusion: ST changes were present in all five cases with severe metabolic acidosis (umbilical artery pH <?7.00). ST changes occurred in 46% of cases with mild metabolic acidosis. CTG plus ST analysis was more specific in detecting fetal acidemia than CTG alone.     

Usefulness of the examination of fetal blood oxygen saturation (FSpO2) and fetal heart rate (FHR) as a prognostic factor of the newborn outcome

OBJECTIVES: Cardiotocography has become the standard for fetal monitoring in labor. False-positive findings during electronic fetal heart rate monitoring may were not associated with neonatal acidemia. Because of the poor specificity of fetal heart rate monitoring in predicting fetal distress, new methods are being investigated as a way to improve the accuracy of assessing the infant's condition during labor. DESIGN: The aim of this study was to determinate the efficiency of fetal blood oxygen saturation (FSpO2) and computer analysis of the fetal heart rate (Co-CTG) in the late 1-st stage of labor as a prognostic factor of newborn acidemia. MATERIALS AND METHODS: Total 62 subjects were studied. During labors and deliveries fetal oxygen saturation was continuously recorded, with use of Nellecor N-400 fetal pulse oximeter and continous CTG were performed by Hewlett Packard 50A. Transdermal fetal oxygen saturation measurements and CTG results obtained during the labors was analyzed using MONAKO system (ITAM Zabrze). The results were compared with the values of pH and base deficit in the umbilical artery measured just after delivery. RESULTS: The sensitivity, specificity, negative, positive predictive values and Youden factor based on FHR and FSpO2, for prognosis of neonatal acidosis were: 65%, 80%, 16%, 97.5% 60% and 0.135 respectively FHR; and 100%, 60%, 100%, 96.8% and 0.968 respectively FSpO2. CONCLUSIONS: 1. The examination of fetal blood oxygen saturation in the labor is a useful prognostic factor of the newborn outcome. 2. The best predictive value for intrapartum fetal asphyxia with metabolic acidosis was found when fetal pulse oximetry is added to cardiotocography.     

Perspektiven der CTG-Anwendung während der Geburt

Cardiotocography (CTG) is the most frequently used method for fetal surveillance during labor. While a normal CTG usually indicates a reassuring fetal status, a non-reassuring or abnormal fetal heart rate (FHR) does not necessarily equate with fetal hypoxia and/or acidosis. The positive predictive value of CTG for adverse outcome is low and the negative predictive value is high. These features, combined with marked interobserver variation in CTG interpretation, result in inappropriately high operative delivery rates for non-reassuring fetal status. Using fetal blood sampling (FBS) in labor with non-reassuring CTG can reduce the high false positive rate of FHR patterns. The use of CTG in combination with FBS permits a reduction of neonatal seizures and also a reduction of avoidable operative deliveries. The development of online analysis of FHR patterns with a quantification of important parameters by computerized expert systems leads to more reproducible interpretation and more diagnostic reliability. Pathologic findings of the supplementary methods for fetal monitoring during labor, fetal pulse oxymetry and ST-waveform analysis of fetal ECG have a good correlation with fetal acidosis making a reduction of FBS possible.