Is umbilicocerebral ratio better than cerebroplacental ratio for predicting adverse pregnancy and neonatal outcomes?

Objective A secondary analysis of the trial of randomized umbilical and fetal flow in Europe suggested that the umbilicocerebral ratio (UCR) provides better differentiation of neurodevelopmental outcome in the abnormal range compared with that of the cerebroplacental ratio (CPR).1 However, the reported superiority of UCR is controversial.2 This study aimed to compare the CPR and the UCR for predicting operative delivery for presumed fetal compromise and prolonged neonatal unit (NNU) admission in term fetuses suspected to be small for gestational age (SGA). Study Design This study was a retrospective analysis of singleton pregnancies with estimated fetal weight less than the 10th centile (SGA) at 36 weeks’ gestation or beyond at St George’s Hospital in London between 1999 and 2015. CPR was calculated as the ratio of middle cerebral artery and umbilical artery pulsatility index, whereas UCR was calculated as the inverse of CPR. The outcomes were operative delivery for presumed fetal compromise and prolonged NNU admission (admission to the NNU for longer than 48 hours).3 Multiples of medians (MoMs) were calculated using the reference ranges reported by Acharya et al.4 The predictive accuracy was assessed using receiver operating characteristic curves. Results The analysis included 958 pregnancies. The incidence rates of operative delivery and prolonged NNU admission were 17.6% (169 of 958) and 4.7% (45 of 958), respectively. The CPR (median: 1.63 vs 1.51) and UCR (median: 0.61 vs 0.66) values were significantly different in fetuses who underwent operative delivery for presumed fetal compromise compared with those who did not (P=.015 for both). There were no statistically significant differences in either UCR or CPR between those with and without prolonged NNU admission (P=.230 for both). The number of outlier values without MoM correction was significantly more with UCR compared with CPR in those who did not have operative delivery for presumed fetal compromise (5.6%, 44 of 789, vs 1.6%,13 of 789; P<.001) and prolonged NNU admission (5.0%, 46 of 913, vs 1.5%, 14 of 913; P<.001). The area under the curve (AUC) values of UCR and CPR for predicting operative delivery for presumed fetal compromise (AUC, 0.56; 95% confidence interval [CI], 0.51–0.61) and prolonged NNU admission (AUC, 0.55; 95% CI, 0.46–0.64) were the same (Figure)