There is increasing evidence it is time we rethought our approach to CTG interpretation. There is little evidence that classifying decelerations into early, late, and different types of variable decelerations is useful as all occur as compensatory mechanisms for low oxygen levels (Xodo, et al., 2022). Instead, it seems more useful to measure “deceleration area under the curve”: a cumulative measure of the amount of time the fetal heart is below the baseline that also considers how deep the deceleration is.
New research from Israel adds to the evidence base (Geva, et al., 2022). Previous researchers have explored the relationship between deceleration area under the curve and cord blood acidosis at birth, finding a correlation. Higher total deceleration area under the curve is associated with lower pH at birth. Geva’s team have added new information looking at the relationship between deceleration area under the curve and the incidence of hypoxic ischaemic encephalopathy. In addition to looking at to looking at deceleration area under the curve, they also looked at acceleration area under the curve (a measure of time above the baseline and the height of accelerations).
Their research used a retrospective case-control approach in a single maternity unit. 95 cases of hypoxic ischaemic encephalopathy in infants born to women considered low risk were identified, with the births occurring between 2013 and 2019. In choosing only a low risk population, the researchers were hoping to exclude infants exposed to hypoxic injury in the antenatal period. 62 cases provided data suitable for analysis as there was a sufficient duration (at least 60 minutes) of CTG monitoring for analysis. These cases were matched with 123 controls with the same gestational age and cord pH at birth. There were no differences between cases and controls with respect to maternal age, BMI, nulliparity, or previous birth by caesarean section. Oxytocin use was more common in cases, as was birth before the second stage of labour. Noninstrumental vaginal birth occurred more often in the controls.
The total deceleration area under the curve was significantly higher in cases than controls as was the deceleration depth. Accelerations were present in 94% of CTG traces for controls and 82% for cases, a significant difference. Total acceleration area above the curve was also significantly larger for controls. Rates of tachycardia were the same in both groups.
The authors note their data provide no information about the specific timing of the hypoxic event, only the timing of the response in the form of changes in the heart rate pattern. They did not seek to identify a discriminatory threshold level of deceleration area under the curve that could distinguish between health infants and those with hypoxic injury. There are may steps yet to go before deceleration area is ready for use in daily clinical practice. This paper provides a useful step along the way.
References
Geva, Y., Yaniv Salem, S., Geva, N., Rotem, R., Talmor, M., Shema, N., Shany, E., & Weintraub, A. Y. (2022, Dec 26). Intrapartum deceleration and acceleration areas are associated with neonatal encephalopathy. International Journal of Gynaecology & Obstetrics, in press. https://doi.org/10.1002/ijgo.14638
Xodo, S., & Londero, A. P. (2022). Is it time to redefine fetal decelerations in cardiotocography? Journal of Personalized Medicine, 12(10). https://doi.org/10.3390/jpm12101552
Categories: CTG, EFM, New research, Perinatal brain injury
Tags: Acceleration area, caesarean section, Deceleration area, HIE, pH, Physiology
Birth Small Talk 
Thanks. Was the time taken to administer postnatal events noted? How do we know its not a confounder if big decelerations are followed by earlier cord clamping before institution of breathing or respiration?
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The CTGs were all from the 120 minutes prior to birth. They used a common definition for HIE (birth event suggesting hypoxia or low Apgar or pH < 7.0 AND neurological signs). They don't comment on cord management practices at the time of birth, and I'm not familiar with standard practice in Israel. Yes – it remains a potential confounder. Clinical practices are always going to confound this sort of research because the databases all use CTGs that were visible to clinicians and part of their decision making.
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Do you think that the time has come to say that ALL research that does not detail the postnatal events should be discounted? Esp given we have evidence that there are dramatic differences in weight in the babies in immediate/’early’/’delayed’ clamping groups. The confounder must surely mess up everything (including the medico-legal paradigm).
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Yes. All the CTG vs IA trials probably need a do-over. I doubt it will happen. But perhaps we can convince researchers to collect some of these important events as data and check to see if they need to correct their findings when these act as confounders.
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Kirstin, I am a member of the Association of Radical Midwives in the UK. We would so love you to speak at our conference in November entitled ‘Hands Off Midwifery: power, politics and practice’. Your research fits all the boxes and we are trying to raise awareness in the UK against huge vested interests, lawyers, tech companies, clinicians, HR and hospital administrators. Probably a forlorn hope but we remain radical. Could you please get in touch with me at margaret.jowitt@talktalk.net or enquiries@midwifery.org.uk. (My own passion is maternal position and the restrictions placed on it by CTG and also, but as yet unconfirmed, that the tightness of the belts abolishes any hope of the fetus ‘steering’ himself into position for second stage.)
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Hi Margaret, I have sent you an email.
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