Intrapartum electronic fetal monitoring and perinatal outcomes: Analysis of components of fetal heart rate pattern

Minakshi Kumari; Anuja Abraham; Kavitha Abraham; Preethi Navaneethan; Reka Karuppusami; Santhanam Sridhar; Annie Regi

doi:10.4103/cmi.cmi_75_22

ORIGINAL ARTICLE

Year : 2023 | Volume : 21 | Issue : 1 | Page : 26-30

Intrapartum electronic fetal monitoring and perinatal outcomes: Analysis of components of fetal heart rate pattern

Minakshi Kumari¹, Anuja Abraham¹, Kavitha Abraham¹, Preethi Navaneethan¹, Reka Karuppusami², Santhanam Sridhar³, Annie Regi¹
¹ Department of Obstetrics and Gynaecology, Christian Medical College, Vellore, Tamil Nadu, India
² Department of Biostatistics, Christian Medical College, Vellore, Tamil Nadu, India
³ Department of Neonatology, Christian Medical College, Vellore, Tamil Nadu, India

Date of Submission	12-Jul-2022
Date of Decision	30-Aug-2022
Date of Acceptance	19-Sep-2022
Date of Web Publication	17-Jan-2023

Correspondence Address:
Dr. Preethi Navaneethan
Department of Obstetrics and Gynaecology, Christian Medical College, Vellore - 632 004, Tamil Nadu
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/cmi.cmi_75_22

Abstract

Aim: The aim of this study was to assess the components of cardiotocography (CTG) during labor to identify the variables associated with the risk of adverse perinatal outcomes and to ascertain the mode of delivery in these women. Materials and Methods: This prospective observational study included 191 women at term with singleton pregnancy in labor. The CTG findings including baseline heart rate, accelerations, beat-to-beat variability, and type and severity of decelerations were noted as per the International Federation of Gynecology and Obstetrics classification and grouped into Category II or III patterns as per the National Institute of Child Health and Human Development classification. Low APGAR score, cord PH <7, neonatal intensive care unit admission, respiratory distress, and hypoxic-ischemic encephalopathy were considered adverse neonatal outcomes. Results: Persistent fetal tachycardia, poor beat-to-beat variability, and severe variable deceleration showed a significant association with adverse neonatal outcome and delivery by cesarean section (P < 0.05). Adverse neonatal outcomes were noted in 4.2% of babies and 40.9% of babies born to mothers whose CTG was categorized as II and III patterns, respectively (P < 0.001). Birth by cesarean section was significantly different between those with Category II and Category III patterns, 33.7% and 65.4%, respectively (P < 0.01). Conclusion: Reduction in the beat-to-beat variability and presence of severe variable decelerations are independent risks for adverse neonatal outcomes, irrespective of the category of CTG pattern. Category III fetal heart rate pattern shows a significant association with adverse outcomes and risk of cesarean delivery. Grading the Category II patterns may help in identifying variables that are truly associated with acidemia and further research into this is recommended.

Keywords: Cardiotocography, deceleration, fetal heart rate, fetal monitoring, pregnancy outcome

How to cite this article:
Kumari M, Abraham A, Abraham K, Navaneethan P, Karuppusami R, Sridhar S, Regi A. Intrapartum electronic fetal monitoring and perinatal outcomes: Analysis of components of fetal heart rate pattern. Curr Med Issues 2023;21:26-30

How to cite this URL:
Kumari M, Abraham A, Abraham K, Navaneethan P, Karuppusami R, Sridhar S, Regi A. Intrapartum electronic fetal monitoring and perinatal outcomes: Analysis of components of fetal heart rate pattern. Curr Med Issues [serial online] 2023 [cited 2023 Jun 7];21:26-30. Available from: https://www.cmijournal.org/text.asp?2023/21/1/26/367863

Introduction

Parturition can be a state of progressive acidemia. Repeated contractions increase the intrauterine pressure and bearing down efforts increase the intra-abdominal pressure, which interferes with placental microcirculation. This leads to hypoxia in the fetus, which, if prolonged, leads to fetal acidemia, neonatal encephalopathy, and cerebral palsy.^[1],[2] The objective of intrapartum fetal surveillance using cardiotocography (CTG) is to monitor fetal heart rate (FHR) alterations to detect fetal acidemia before irreversible fetal damage occurs.

The limitations of continuous electronic fetal monitoring (EFM) are high interobserver variability and high false-positive rate (60%), where the abnormal FHR pattern does not translate into fetal hypoxia.^[3],[4] The Category II pattern of the National Institute of Child Health and Human Development (NICHD) classification is very wide and heterogeneous but most often not predictive of fetal hypoxemia.^[5] The purpose of this study was to assess the components of the CTG to identify the variables related to the risk of adverse perinatal outcomes and to ascertain the mode of delivery in laboring women.

Materials and Methods

Study design

This was a prospective observational study.

Setting

This study was done in the labor ward in a tertiary referral center in South India.

Period

The duration of the study was between December 2016 and September 2017.

Inclusion criteria

Women at term gestation with singleton pregnancy and fetus in cephalic presentation admitted in the labor room were eligible for the study. We included women with spontaneous labor and those with induced labor. All women in the labor room underwent continuous CTG monitoring for intrapartum fetal surveillance.

Ethical consideration

This study was approved by the Institutional Review and Ethics Committee, approval IRB Min. No. 10418, dated December 03, 2016. Written informed consent in English and Tamil (regional language) was obtained from all the study participants.

Variables and data source

Categorization of CTG tracings as Category I (normal), Category II (indeterminate), and Category III (abnormal) was according to the three-tier FHR interpretation system suggested by the NICHD 2008 workshop.^[6] Women with CTG tracings identified Category II and III FHR patterns as per the NICHD criteria were enrolled in the study after written informed consent. Women who were likely to have adverse neonatal outcomes or anticipated need for neonatal resuscitation including placental abruption, cord prolapse, previous cesarean section, fetal anomaly including congenital diaphragmatic hernia, and fetal growth restriction with abnormal umbilical artery Doppler were excluded. The demographic details including age, parity, obstetric and medical risk factors, details of onset of labor, indication and method of induction and oxytocin usage for augmentation of labor, and presence of meconium-stained amniotic fluid were documented. Hyperstimulation requiring acute tocolysis with terbutaline and utilization of amnioinfusion in case of severe recurrent variable decelerations with clear liquor were also recorded in the pro forma.

The components of CTG including the baseline heart rate, accelerations, beat-to-beat variability, and decelerations were noted as defined by the International Federation of Gynecology and Obstetrics classification for CTG and then categorized into Category II or III FHR patterns according to the NICHD classification. The severity of the deceleration and the duration of the abnormal CTG pattern were also recorded. The individual components of the CTG were assessed to identify the correlation with the degree of neonatal depression, if present. Severe variable decelerations were defined as a deceleration with FHR dropping to 60 bpm and the duration lasting more than 60 s. Cord blood gases were done when the APGAR scores were low and the baby was depressed at birth requiring resuscitation. APGAR score <7 at 5 min, cord pH <7, neonatal intensive care unit admission, respiratory distress syndrome, hypoxic-ischemic encephalopathy (HIE), tachypnea, and prolonged hospital stay were considered adverse neonatal outcomes.

Study size

Based on the observational study by Holzmann et al.,^[7] to study the perinatal outcome with each component of CTG tracing with the expected proportion of 0.144 (14.4%) with a precision of 5% and 95% confidence interval, the sample size of 190 women was calculated.

Statistical methods

Descriptive statistics, mean ± standard deviation, were obtained for continuous data, while the frequencies and percentage were obtained for categorical data. The Chi-square and Fisher's exact tests (less cell frequency) were applied to the data. All tests were two-sided and α = 0.05 was taken as the level of significance. Statistical analysis was done using IBM SPSS statistics for Windows Version 21.0 (Armonk, NY, USA: IBM Corp).

Results

A total of 191 women were recruited for the study after informed written consent. The demographic variables of the participants are presented in [Table 1]. The mean age was 26 years, and the mean gestational age at delivery was 39 weeks. The mean birth weight of the babies born was 2924 g.

Table 1: Demographic characteristics

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Most of the women were primiparous (84.8%), and more than half of the women (62.3%) underwent induction of labor. Among those who were induced, 84.3% (n = 161) of women required labor augmentation with oxytocin. Of the 191 women, 37.2% (n = 71) of women underwent cesarean section and 62.8% (n = 120) of women had vaginal delivery; 60.7% of the latter group were operative vaginal delivery.

Of the 169 mothers with Category II FHR patterns, 4.2% of babies (n = 7) and, of the 22 mothers with Category III FHR patterns, 40.9% of babies (n = 9) had adverse neonatal outcomes (P ≤ 0.001) [Table 2]. The need for cord pH due to babies born depressed at birth and low APGAR scores was 6.7% in those with Category II tracing and 50% in those with Category III tracing (P < 0.001). Birth by cesarean section was also significantly different between those with Category II and Category III FHR patterns; 33.7% (n = 57) of patients with Category II and 65.4% (n = 14) of patients with Category III tracing had cesarean section (P < 0.01).

Table 2: Association of fetal heart rate categories with the fetal and maternal outcomes

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The individual components of the CTG were analyzed for association with adverse perinatal outcome and need for cesarean delivery [Table 3]. Persistent fetal tachycardia, poor beat-to-beat variability, and severe variable deceleration were found to be significantly associated with adverse neonatal outcome (P < 0.05). A similar relationship between the need for cesarean section among those with CTG findings of poor variability, persistent tachycardia, and severe variable decelerations was found. The association remained significant even after univariate and multivariate logistic regression analyses. The variables associated with adverse neonatal outcome and cesarean section remained statistically significant in the background of both clear liquor and meconium-stained liquor.

Table 3: Association of components of cardiotocogram with adverse neonatal outcome and mode of delivery

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There was no significant difference in the neonatal outcome and need for cesarean section in those who had tachysystole with or without fetal heart changes [Table 4]. Although there was no statistical difference in the neonatal outcome when the CTG findings were observed in the background of clear liquor or meconium-stained liquor, the presence of meconium-stained amniotic fluid significantly increased the likelihood of needing a cesarean section (P = 0.03). Of the 26 women who received amnioinfusion for severe variable deceleration, only 2 (7.7%) babies were depressed at birth, and this was not found to be statistically significant (P = 1.00).

Table 4: Association of neonatal outcome and mode of delivery with other variables

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Discussion

The FHR is balanced by the autonomic nervous system of the fetus, in which the parasympathetic system matures by term gestation and the sympathetic system continues to develop. This maturation is noted as a decrease in heart rate and an increase in the beat-to-beat variability toward term. The various external factors including the fetal oxygenation levels which further affect the fetal pH play an important role in the FHR patterns.^[1]

Intrapartum FHR variations that occur in the presence of uterine contractions reflect variation in the placental circulation and perfusion in the fetus. EFM using CTG is a simple method available for intrapartum fetal surveillance and thereby predicts fetal hypoxia. However, prior studies including the Cochrane review on continuous EFM have shown reduced rates of neonatal seizures. No other neonatal outcome improved significantly, but EFM resulted in an increase in the cesarean section rates.^[8]

Among the 191 women included in this study, 88.5% were classified as Category II and 11.5% as Category III. This finding was similar to various studies which noted that ≥80% of the CTG patterns fall into Category II in labor and only 16% of fetuses will remain in Category I pattern till delivery.^[9],[10]

In a case–control study done by Larma et al., an association between CTG patterns and neonatal outcomes including metabolic acidemia, hypoxemic ischemic encephalopathy, and asphyxia was studied. It was noted that fetal bradycardia and variability <5 bpm had a significant association with HIE.^[2] In the present study, fetal patterns with persistent tachycardia, poor beat-to-beat variability, and severe variable deceleration were significantly associated with adverse neonatal outcomes (P < 0.05).

Pattern recognition software was used to analyze the digital FHR tracing to identify the various patterns of variable decelerations associated with metabolic acidemia at birth in a study done by Hamilton et al.^[10] According to that study, acidemia was significantly related to the variable deceleration with “sixties” criteria which include deceleration to a depth of 60 bpm and the duration of the deceleration lasting for 60 s or more and loss of variability during the deceleration. Similarly, in our study, the variable deceleration as such was not noted to have adverse neonatal outcomes, but substantial association was seen in those with severe variable decelerations. Cesarean section rates were high in those with variable decelerations, but this may not translate into better outcomes.

According to William et al., poor variability for at least an hour with or without late decelerations was linked to acidemia in 24%–31% of patients.^[11] A study by Holzmann et al. showed that fetal acidemia was associated with late decelerations and severe variable decelerations but not those with isolated poor variability.^[7] However, in the present study, poor variability was significantly associated with both adverse neonatal outcome and risk of cesarean delivery. Limitation in our study is the lack of data indicating whether poor variability was observed alone or in conjunction with other abnormal patterns. Another limitation of our study is that we did not analyze each component of CTG based on the duration of abnormality. The study included women with obstetric risk factors including preeclampsia and diabetes complicating pregnancy, and considering that more than half of those in the study were induced, the indication for induction could have also played a role in the decision for cesarean section.

Cesarean delivery was done in 37.7% of those with FHR abnormality. This rate was higher compared to the study done by Gangwar et al., where it was 18.02%.^[12] We do not have the facility for fetal blood sampling and computerized analysis of the CTG patterns, which may have contributed to the increased cesarean section rates in those with CTG abnormalities. However, a systematic review by Balayla et al. noted that utilizing artificial intelligence for intrapartum fetal tracing did not enhance neonatal outcomes nor modify the mode of delivery.^[13]

Understanding the heterogeneity of the Category II tracings, various authors had tried to risk stratify the fetal heart tracing based on the estimated fetal weight and presence of other obstetric risk factors including meconium-stained amniotic fluid to improve the neonatal outcomes and to recognize the true FHR variations associated with fetal metabolic acidemia.^[14],[15] In the present study, women with meconium-stained liquor had significantly higher rates of cesarean delivery (P = −0.03). Adverse neonatal outcome was high in this group but was not statistically significant.

Conclusion

Reduction in the beat-to-beat variability and presence of severe variable decelerations are independent risks for adverse neonatal outcomes, regardless of the CTG category. Category III FHR pattern shows a significant association with adverse outcomes and risk of cesarean delivery. CTG, if appropriately interpreted, helps in identifying the mechanical and hypoxic stress along with the fetal compensatory status. As there are limitations to the current categorization of the CTG in identifying fetus at risk of HIE, metabolic acidemia, and asphyxia, the understanding of the various components in the FHR and identifying the variables most often related to adverse neonatal outcomes will definitely help in managing labor complicated by alterations in the FHR without increasing the risk of cesarean section. Grading the Category II tracing may help in identifying patterns that are truly associated with acidemia and further research into this is recommended.

Research quality and ethics statement

All authors of this manuscript declare that this scientific study is in compliance with standard reporting guidelines set forth by the EQUATOR Network. The authors ratify that this study required the Institutional Review Board/Ethics Committee review, and hence, prior approval was obtained IRB Min. No. 10418, dated December 03, 2016). We also declare that we did not plagiarize the contents of this manuscript and have performed a plagiarism check.

Acknowledgments

The authors would like to thank Ms. Bhanu Sankaran for her technical support.

Financial support and sponsorship

This study was financially supported by the Institutional Fluid Research Grant.

Conflicts of interest

There are no conflicts of interest.

References

1.	Jayasooriya G, Djapardy V. Intrapartum assessment of fetal well-being. BJA Educ 2017;17:406-11.
2.	Larma JD, Silva AM, Holcroft CJ, Thompson RE, Donohue PK, Graham EM. Intrapartum electronic fetal heart rate monitoring and the identification of metabolic acidosis and hypoxic-ischemic encephalopathy. Am J Obstet Gynecol 2007;197:8.e1-8.
3.	Clark SL, Hamilton EF, Garite TJ, Timmins A, Warrick PA, Smith S. The limits of electronic fetal heart rate monitoring in the prevention of neonatal metabolic acidemia. Am J Obstet Gynecol 2017;216:163.e1-163.e6.
4.	Pinas A, Chandraharan E. Continuous cardiotocography during labour: Analysis, classification and management. Best Pract Res Clin Obstet Gynaecol 2016;30:33-47.
5.	Ugwumadu A. Are we (mis) guided by current guidelines on intrapartum fetal heart rate monitoring? Case for a more physiological approach to interpretation. BJOG 2014;121:1063-70.
6.	Macones GA, Hankins GD, Spong CY, Hauth J, Moore T. The 2008 national institute of child health and human development workshop report on electronic fetal monitoring: Update on definitions, interpretation, and research guidelines. Obstet Gynecol 2008;112:661-6.
7.	Holzmann M, Wretler S, Cnattingius S, Nordström L. Cardiotocography patterns and risk of intrapartum fetal acidemia. J Perinat Med 2015;43:473-9.
8.	Alfirevic Z, Devane D, Gyte GM, Cuthbert A. Continuous cardiotocography (CTG) as a form of electronic fetal monitoring (EFM) for fetal assessment during labour. Cochrane Database Syst Rev 2017;2:CD006066.
9.	Clark SL, Nageotte MP, Garite TJ, Freeman RK, Miller DA, Simpson KR, et al. Intrapartum management of category II fetal heart rate tracings: Towards standardization of care. Am J Obstet Gynecol 2013;209:89-97.
10.	Hamilton E, Warrick P, O'Keeffe D. Variable decelerations: Do size and shape matter? J Matern Fetal Neonatal Med 2012;25:648-53.
11.	Williams KP, Galerneau F. Intrapartum fetal heart rate patterns in the prediction of neonatal acidemia. Am J Obstet Gynecol 2003;188:820-3.
12.	Gangwar R, Chaudhary S. Caesarean section for foetal distress and correlation with perinatal outcome. J Obstet Gynaecol India 2016;66:177-80.
13.	Balayla J, Shrem G. Use of artificial intelligence (AI) in the interpretation of intrapartum fetal heart rate (FHR) tracings: A systematic review and meta-analysis. Arch Gynecol Obstet 2019;300:7-14.
14.	Eller AG, Esplin MS. Management of the category II fetal heart rate tracing. Clin Obstet Gynecol 2020;63:659-67.
15.	Frey HA, Tuuli MG, Shanks AL, Macones GA, Cahill AG. Interpreting category II fetal heart rate tracings: Does meconium matter? Am J Obstet Gynecol 2014;211:8.e1-8.