Introduction
Cardiotocography (CTG), also referred to as electronic foetal monitoring (EFM), is the most widely used non-invasive foetal heart rate (FHR) monitoring before and during labour 1, 2. Foetal hypoxia and acidosis could be detected primarily through the recognition of specific patterns on the CTG signal (e.g., decelerations)3-5. These CTG patterns, however, are difficult for human visual interpretation to reliably and consistently identify1, 6, 7. It is well-established that subjective assessment of the CTG patterns suffers from poor inter-observer and intra-observer reproducibility 1, 8-13 and is associated with increased operative vaginal delivery and Caesarean section rates without improving perinatal outcomes 14, 15. Computerised cardiotocography (cCTG) has been considered to be superior to conventional CTG as this approach provides more reliable and consistent interpretation of the CTG tracing 1, 2, 16, 17. Based on specific criteria of Dawes-Redman system, cCTG enables quantitative and objective evaluation of the foetal state1, 2. Results from earlier studies comparing human visual analysis and computerised analysis of FHR tracing supported the idea that computerised analysis could overcome the subjectivity of visual interpretation of FHR tracing 18, 19.
Short-term variation (STV) is the measurement of beat-to-beat variation in the FHR over a very short time scale provided by cCTG20. A study demonstrated that the risk of metabolic acidaemia increased as the antepartum cCTG STV decreased; at the optimal cut-off level at 3.0 milliseconds or less, the positive and negative predictive values were 64.6% and 86.6%, respectively21. The Dawes-Redman approach has the advantages of enabling objective evaluation of cCTG STV and analyzing the CTG trace with information on foetal movements, presence of sinusoidal patterns, and quality of the electronic tracing 1. It has been observed that there is increasing use of cCTG for the evaluation of foetal wellbeing especially for high-risk cases, including those with foetal growth restriction (FGR) and preeclampsia 2, 16, 22. As such, the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) has integrated the use of cCTG STV in a recent guideline for the monitoring and management of pregnancies with FGR22.
Doppler velocimetry by examining the uterine artery pulsatility index (UtA-PI), umbilical artery pulsatility index (UA-PI), middle cerebral artery pulsatility index (MCA-PI) and cerebroplacental ratio (CPR) (which is the ratio between MCA-PI and UA-PI), can evaluate uteroplacental function and allow for the detection of uteroplacental insufficiency 23-26. These Doppler indices are important in the diagnosis, monitoring, and management of high-risk pregnancies especially for those with FGR 22, 27-29. In addition, evidence shows that monitoring and delivery timing according to a specific protocol including Doppler indices and cCTG provide better-than-expected outcomes for fetuses diagnosed with FGR30.
Despite solid evidence supporting the use of cCTG and Doppler velocimetry in the management of pregnancies complicated with FGR, there is a scarcity of data on the clinical utility of cCTG and Doppler velocimetry in pregnancies in other clinical scenarios, such as during latent phase of labour or before induction of labour. This study aimed to investigate the relationship and the potential value of prelabour maternal-foetal Dopplers and cCTG STV in predicting labour outcomes including umbilical cord arterial pH, emergency delivery due to pathological CTG during labour and neonatal intensive care unit (NICU)/special care baby unit (SCBU) admission.