Interpretation
Despite the association between abnormal conventional CTG and poor perinatal outcomes, the use of CTG has not been shown to improve perinatal outcomes 1, 16. In an attempt to overcome the disadvantages of traditional CTG monitoring, the cCTG, which is an advanced electronic assessment of FHR, has been introduced. The clinical usefulness of the cCTG as a routine prelabour screening technique for foetal well-being remains debatable. Our initial study demonstrated that admission maternal-foetal Doppler indices, cCTG STV and Dawes-Redman criteria were not predictive of composite neonatal morbidity. However, we demonstrated a significant correlation between mean UtA-PI and umbilical cord arterial base excess but not pH, suggesting the former might be a better reflection of placental reserve/function during labour. Further, it was observed that there was a trend toward a reduction in composite neonatal morbidities (arterial cord blood pH < 7.1, base excess ≤ -12 mmol/L, Apgar score ≤ 5 at 5 min and/or NICU admission) with increasing log10 cCTG STV (odds ratio, 0.074; 95%CI, 0.005–1.128, p = 0.061)16.
In the current study, the finding that there was a significant positive correlation between log10 cCTG STV and umbilical cord arterial pH agrees with a previous study by Bellver et al .36. There was no association between log10 cCTG STV and emergency delivery due to pathological CTG during labour (n = 34) and between log10 cCTG STV and umbilical cord arterial pH < 7.1 (n = 10) which could be attributed to the low rates of these two outcomes. Women who required emergency delivery due to pathological CTG during labour, compared to those that did not, had significantly lower MCA-PI and MCA-PI z-score. These findings may represent foetal cerebral vasodilatation, a haemodynamic response to foetal hypoxaemia to increase blood supply to the brain (known as the brain sparing effect). As expected, neonatal outcomes were poorer in newborns that required emergency delivery due to pathological CTG during labour. In this study, 40% and 83% of emergency deliveries due to pathological CTG during labour had umbilical cord arterial pH <7.1 and required NICU admission, respectively. There was also a significant negative correlation between umbilical cord arterial pH and smoking; however, direct effect of smoking on umbilical cord arterial pH has not been previously demonstrated. Oncken et al. reported no difference between umbilical cord arterial pH between smokers and non-smokers. Whilst Tarasi et al. reported that smoking appeared to be a protective factor for umbilical cord arterial pH < 7.137. Chronic or acute hypoxia and the presence of carbon monoxide in the maternal circulation from smoking could result in altered oxygen delivery and be harmful to the fetus38. Nonetheless, the correlation between smoking and umbilical cord arterial pH needs further exploration.
The predictors for NICU/SCBU admission were nulliparity, maternal diabetes and EFW z-score; with the latter two being related to neonatal hypoglycemia in pregnancies complicated by maternal diabetes. Increased maternal BMI also demonstrated a tendency toward increasing the risk of NICU/SCBU admission, although it was not statistically significant. This finding may emphasise the importance of adequate glycemic control during pregnancy. While nulliparous women are more likely to have a longer labour and labour complications compared to parous women39, as a result, their infants have an increased risk of NICU/SCBU admission.
Our findings are comparable to that of a study by Fratelli et al. which demonstrated no predictive value of pre-induction maternal-foetal Doppler indices (z-scores of UtA-PI, UA-PI, and MCA-PI) for operative delivery for intrapartum foetal compromise or umbilical cord arterial pH < 7 in a cohort of appropriately grown fetuses undergoing induction of labour in an unselected population 40. Pre- or early labour assessment of maternal-foetal Dopplers, log10 cCTG STV, and Dawes-Redman criteria may not be reliable tools to either predict or exclude intrapartum acidosis and ensure a favourable labour outcome. These findings could be explained by the fact that labour outcome is influenced by several intrapartum events and variable foetal response to intrauterine stress.
Conclusions: In consecutive women with singleton pregnancy admitted during latent phase of labour or for induction of labour at term, MCA-PI, and MCA-PI z-score are significant lower in pregnancies that require emergency delivery for pathological CTG during labour compared with those who do not. cCTG STV is associated with umbilical cord arterial pH but not predictive of emergency delivery due to pathological CTG during labour. None of the factors amongst maternal characteristics, labour onset, indications of labour induction, EFW, maternal-foetal Doppler indices, cCTG STV and Dawes-Redman criteria by cCTG is predictive for umbilical cord arterial pH < 7.1 and emergency delivery due to pathological CTG during labour. This study has demonstrated that unfavourable labour outcomes cannot be anticipated by routine prelabour maternal-foetal Doppler velocimetry and cCTG assessment, thus further research is necessary to identify potential predictors of labour outcomes.
Table 1. Characteristics of the study population regarding emergency delivery due to pathological CTG during labour status