Antenatal cardiotocography for fetal assessment
The review found no clear evidence that in high-risk pregnancies fetal assessment by antenatal cardiotocography benefits either the mother or her fetus. Clinicians need to know that, although this intervention may not increase a woman’s chance of having a caesarean section, it does not prevent the risk of perinatal death either.
RHL Commentary by Okusanya BO
Antenatal cardiotocography (CTG) is a screening method used in pregnancy to identify fetuses at risk of developing hypoxia. Based on data from observational studies, it was originally thought that CTG would be an asset in detecting early poor fetal outcomes, indicating the need for interventions to help improve chances of survival for newborn infants (1). However, available data suggest that when CTG is used as the “non-stress test” or the “contraction stress test”, it can lead clinicians to use unnecessary or inappropriate interventions as a result of intraobserver and interobserver errors associated with its visual interpretation. In high-risk pregnancies, non-reactive CTG may even be associated with increased fetal morbidity and mortality (2). Owing to the errors associated with visual interpretation of CTG results, a computerized method of analysis has been developed, which gives a more objective and reliable interpretation (3).
Developing countries account for most of the global burden of perinatal deaths (4, 5), but at the present time the use of antenatal CTG in under-resourced settings is limited. An evaluation of antenatal CTG in Nigeria found that women who received a non-reactive non-stress test were significantly more likely to deliver by caesarean section, experience high perinatal mortality, and have small-for-gestational-age infants; the authors of that study concluded that the non-reactive non-stress test was a valuable tool for early detection of fetal compromise (6). Evaluation of antenatal CTG is important because its use may increase in under-resourced settings in the future as more obstetric units procure the equipment. This Cochrane review (7) evaluated the effectiveness of antenatal CTG for monitoring the fetus in high-risk pregnancies with the aim of improving perinatal outcomes.
2. METHODS OF THE REVIEW
The review authors sought to compare no CTG with traditional CTG, on one hand, and traditional CTG with computerized CTG, on the other. They seached the Cochrane Central Register of Controlled Trials and MEDLINE databases for randomized and quasi-randomized trials that had compared antenatal cardiotocography (including, computerized CTG analysis) with alternative methods. In addition, relevant hand-searched articles and conference proceedings were also reviewed for eligibility. The identified studies were assessed for adequate sequence generation, allocation concealment and blinding.
The inclusion and exclusion criteria used in this review conformed to those of the Cochrane review system. The authors reported no heterogeneity or reporting bias, but because of insufficient data, no subgroup analysis was done for low-risk versus high-risk pregnancies, singleton versus multiple gestation, and CTG monitoring prior to 37 weeks of gestation versus CTG monitoring after 37 weeks of gestation.
Primary outcomes for the review were perinatal mortality and caesarean section, and secondary outcomes were potential perinatal mortality, Apgar score of less than seven at five minutes, admission to a neonatal intensive care unit, gestational age at birth and neonatal seizures.
3. RESULTS OF THE REVIEW
Six studies involving 2105 women were included in the review. Four studies (1656 women) compared antenatal CTG with no CTG, while the other two studies (469 women) compared traditional CTG with computerized CTG analysis. All included studies were not of high quality; two studies had adequate sequence generation and allocation concealment, but blinding in all studies was inadequate.
When compared with no CTG, traditional CTG use resulted in no significant difference in the risks of perinatal mortality and caesarean section for women. As regards the secondary outcomes, traditional CTG did not significantly affect Apgar scores less than seven at five minutes, admission to a neonatal intensive care unit, and neonatal seizures; moreover, it had no impact on gestational age at birth.
However, compared with traditional CTG, the use of computerized CTG was associated with a significant reduction in perinatal mortality [relative risk (RR) 0.20; 95% confidence interval (CI) 0.004–0.88], although there was no difference in the risk of caesarean section for women, detection of potentially preventable perinatal mortality (mortality from factors other than lethal congenital abnormalities), Apgar scores of less than seven at five minutes, length of stay in a neonatal intensive care unit or the gestational age at birth.
4.1. APPLICABILITY OF THE RESULTS
This systematic review found no clear evidence that in high-risk pregnancies fetal assessment by antenatal CTG benefits either the mother or her fetus. Although antenatal CTG may not increase a woman’s chance of having a caesarean section, it does not prevent the risk of perinatal death either. The available evidence for the benefit of traditional antenatal CTG in high-risk pregnancies makes its difficult to recommend its use for fetal assessment. Moreover, the reduction of perinatal death associated with the use of computerized CTG was compromised by the low quality of the studies included in the review. The non-inclusion of studies performed in low-income countries makes the effectiveness of antenatal CTG in these settings uncertain.
4.2. IMPLEMENTATION OF THE INTERVENTION
Available evidence for the use of antenatal cardiotocography (CTG) during pregnancy to identify fetuses at the risk of hypoxia is not sufficient to warrant any change in practice.
4.3. IMPLICATIONS FOR RESEARCH
In the light of current evidence, new research on antenatal CTG should focus on specific complications in pregnancy in order to evaluate the usefulness of antenatal CTG in those conditions. Also, its use in both high-income and low-income settings needs evaluation. There is an urgent need for further evaluation of computerized CTG despite the available evidence which supports its effectiveness. Finally, the need to evaluate women’s view and their satisfaction with CTG should not be neglected.
- Freeman RK, Anderson G, Dorchester W. A prospective multi-institutional study of antepartum fetal heart rate monitoring. I. Risk of perinatal mortality and morbidity according to antepartum fetal heart rate test results. American Journal of Obstetrics and Gynecology 1982;143:771-777.
- Boehm FH, Salyer S, Shah DM, Vaughn WK. Improved outcome of twice weekly non stress testing. Obstetrics & Gynecology 1986; 67(4):566-568.
- Dawes GS, Lobb M, Moulden M, Redman CWG, Wheeler T. Antenatal cardiotocography quality and interpretation using computers. British Journal of Obstetrics and Gynaecology 1992; 99:971-977.
- Abu Habib N, Lie RT, Oneko O, Shao J, Bergs P, Daltveit AK. Sociodemographic characteristics and perinatal mortality among singletons in North East Tanzania: a registry-based study. Journal of Epidemiology and Community Health 2008;62:960-965.
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This document should be cited as: Okusanya BO. Antenatal cardiotocography for fetal assessment: RHL commentary (last revised: 1 July 2010). The WHO Reproductive Health Library; Geneva: World Health Organization.