Can the AAT predict outcomes as well as antenatal CTG use?

This is the third post in a series I am writing about the Auscultated Acceleration Test or AAT. If you haven’t been following along and don’t know what this test is – you can read about it here. The goal of antenatal CTG monitoring is to predict which fetuses are at risk of a poor outcome relating to low oxygen levels, so action can be taken and therefore avoid death or long term harm. The research I’m going to look at today set out to answer the question of whether or not the AAT performs as well as antenatal CTG use – also called a non-stress test or NST – at predicting poor outcomes (Paine et al., 1992).

How was the research done?

205 women who had been referred for antenatal CTG monitoring agreed to take part in the research. All had both CTG monitoring and an AAT, with this performed simultaneously in 96.4% of the women. The CTG monitoring was initiated by a different person to the one performing the AAT, who was not aware of the results of the CTG monitoring. When women had more than one round of testing, the results from the tests closest to the time of birth were used in the analysis.

How well the two tests correlated with one another was compared. Test results for both the CTG monitoring and the AAT were then compared to clinical outcomes, looking to see how well each test predicted babies who , developed “fetal distress”, or neonatal morbidity (any one of resuscitation, admission to the nursery, or prolonged hospital stay). And because I know Professor Susan Bewley will email me to ask this question – they provided no information about the timing of cord clamping.

What did they find?

Once again – the accuracy of the midwives performing the AAT was high: with a strong correlation between the baseline heart rate recorded in the AAT and simultaneously on the CTG. When the most recent antenatal CTG was abnormal, 18% of infants developed fetal distress in labour, and 18% experienced neonatal morbidity. When the AAT was abnormal 15% of infants developed fetal distress and 11% neonatal morbidity – the difference with CTG use was not significant.

Looking the other way around – when the most recent CTG was normal 86% of infants did not develop fetal distress, and 97% did not develop neonatal morbidity. For the AAT this numbers were also very similar and not significantly different, at 86% and 99%.

What does this mean?

This research added to what had been shown previously, providing reassurance that not only are heart rates and accelerations equally well detected with the AAT as they are with antenatal CTG monitoring, the AAT performs in a similar way as the CTG for detecting important clinical outcomes.

What do you think? Is it time to breathe life into the AAT once again?

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References

Paine, L. L., Benedict, M. I., Strobino, D. M., Gegor, C. L., & Larson, E. L. (1992, Mar-Apr). A comparison of the auscultated acceleration test and the nonstress test as predictors of perinatal outcomes. Nursing Research, 41(1), 87-91. https://www.ncbi.nlm.nih.gov/pubmed/1549525