Low oxygen levels in labour are considered to place the fetus at risk for permanent injury. One of the organs in the body that rely on high levels of oxygen supply is the heart. Physiological reflexes that manifest as CTG changes are, in part, protective for the fetal heart as they redirect blood from other parts of the body to the heart and brain.
Historically, low oxygen levels in labour were considered to be the most common cause of brain injury leading to long term conditions like cerebral palsy. More recent evidence has shown that cerebral palsy is uncommonly due to low oxygen levels (Philpot, et al., 2020). Less is known about the relationship between fetal heart rate patterns and the potential for damage to the fetal heart. Theoretically, low oxygen levels in labour may cause damage to the muscular layer of the heart leading to poor function.
Recent research from Israel examined outcomes from a population of babies born by caesarean section between 1999 and 2014 (Leybovitz-Haleluya, et al., 2021). 5,810 babies were born by caesarean due to an abnormal fetal heart rate (the terminology used in the paper refers to a non-reassuring fetal heart rate – the specific diagnostic criteria came from the United States National Institute of Child Health and Human Development guidelines). Another 4,146 babies born by caesarean section for slow labour progress and with a normal fetal heart rate pattern formed the comparison group. For all the babies, hospital data about cardiovascular problems leading to admission to hospital was examined up to the age of 18 years. The average follow up time for babies with abnormal heart rate patterns was 8.9 years and for those with normal patterns was 12.3 years.
No differences in any cardiovascular condition were found between the two groups. This remained the case when only babies with low Apgar scores were assessed, and when the sample was controlled for gestational age, low birth weight, and being small for gestational age.
It may be that the follow up period was too short to demonstrate a difference in heart function that might become obvious with aging in later life. It may be that the fetus is remarkably resilient and that compensatory mechanisms that generate the fetal heart rate patterns in labour are sufficient to prevent heart damage.
Leybovitz-Haleluya, N., Wainstock, T., Pariente, G., & Sheiner, E. (2021, Apr). Non-reassuring fetal heart rate patterns: Is it a risk factor for long- term pediatric cardiovascular diseases of the offspring? Early Human Development, 155, 105330. https://doi.org/10.1016/j.earlhumdev.2021.105330
Philpot, P., Greenspan, J., & Aghai, Z. H. (2020). Problems During Delivery as an Etiology of Cerebral Palsy in Full-Term Infants. In Cerebral Palsy (pp. 67-76). https://doi.org/10.1007/978-3-319-74558-9_6
Thank you – this looks very interesting.
Thank you for your blogs. I’m grateful for your work and contribution in this space.
So when we realise that abnormal fetal heart rate patterns are protective of the fetus we will have to conclude that it is a waste of time monitoring them. What do we do then?
Hopefully we can then focus on finding effective care options that actually improve outcomes.