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