I’ve written before about new physiology research suggesting that looking at the time the fetal heart rate is either below (deceleration area) or above (acceleration area) the baseline is a better indicator of fetal wellbeing than current approaches to CTG interpretation. Much of the research about fetal heart rate monitoring looks at surrogate measures rather than clinical endpoints: for example measuring cord blood gas results, or Apgar scores. It is always helpful when researchers go the extra mile and look at clinically important outcomes.
An Israeli based research team have recently explored the relationship between hypoxic ischaemic encephalopathy (HIE) and deceleration and acceleration area – you can read my review of their paper here. The same team have extended their research to include an examination of the relationship between acceleration and deceleration area and the types of brain injury seen on MRI scanning in neonates treated for hypoxic ischaemic encephalopathy. MRI changes are a better predictor of long-term neurological disorders than clinical grading of the symptoms of hypoxic ischaemic encephalopathy, and are far more predictive than cord gases or Apgar scores.
How was the research conducted?
Infants born to women considered low risk in the antenatal period, who were born after 34 weeks of gestation, and who were treated with therapeutic cooling for hypoxic ischaemic encephalopathy were included. There also needed to be at least 60 minutes of CTG recording from the two hours prior to birth, and an MRI of the brain in the first ten days of life. MRI results were graded using a modified Rutherford score and categorised into normal – mild, or moderate – severe. Acceleration and deceleration area was calculated manually by an investigator who was blinded to outcomes.
77 infants met inclusion criteria. Interestingly, oxytocin use was more common in infants with normal – mild MRI findings (69%) than those with moderate – severe findings (42%). Caesarean section was more commonly used for slow labour progress, or for a non-reassuring fetal heart pattern in infants with moderate – severe MRI findings. There were no other statistically significant differences in maternal, labour, or delivery characteristics (though the timing of cord clamping was not reported). One infant (in the moderate – severe MRI group) died.
Did CTG patterns correlate with the MRI findings?
Yes, they did. Total acceleration area was very strongly associated with normal – mild MRI findings. Even the simple presence of accelerations was linked to less abnormal MRI findings, with 82% of infants in the normal – mild MRI category have accelerations in the 2 hours prior to birth, compared to 65% in the moderate – severe category, a statistically significant difference. While there was a trend towards total deceleration area, and tachycardia, being associated with more abnormal MRI findings, these weren’t statistically significant. The ratio of acceleration area to deceleration area was the best predictor of moderate – severely abnormal MRI findings, with a p value of 0.003. This is not a feature of the CTG that a busy clinician can easily spot, but is a calculation that could be performed by computer interpretation of the trace.
How does this translate into practice?
As was the case in their previous research, and that of others working in this space, no threshold measure was identified that reliably distinguished between infants with normal – mild MRI changes and those with moderate – severe changes. While larger acceleration area was associated with a better outcome, it is important to keep in mind that more than half the infants with more severe brain injury findings and a diagnosis of hypoxic ischaemic encephalopathy displayed accelerations on the CTG in the 2 hours leading up to birth. Accelerations should not, therefore, be taken as reassurance that fetal oxygenation is entirely normal. The approach of using acceleration and / or deceleration area in research is helping to provide new insights into fetal physiology, but it is not yet ready for application in the clinical arena.
Reference
Geva, N., Geva, Y., Salem, S. Y., Marks, K. A., Rotem, R., Abramsky, R., Hershkovitz, R., Shelef, I., Novik, E. F., Weintraub, A. Y., & Shany, E. (2023, Mar 24). The association of intrapartum deceleration and acceleration areas with MRI findings in neonatal encephalopathy. Pediatric research, in press. https://doi.org/10.1038/s41390-023-02575-5
Categories: CTG, EFM, New research, Perinatal brain injury
Tags: HIE, Deceleration area, Acceleration area, MRI
Birth Small Talk 
sorry, I cant see behind the paywall, but did the researchers note and put timing of cord clamping into the analysis?
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No they didn’t. It would be lovely if researchers started to take this into account.
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