Poor neonatal acid-base status in term fetuses with low cerebroplacental ratio

Objective: To determine whether small- and appropriate-for-gestational-age (SGA and AGA) term fetuses with a low cerebroplacental ratio (CPR) have worse neonatal acid-base status than those with normal CPR. Methods: This was a retrospective study of 2927 term fetuses divided into groups according to birth-weight centile and CPR multiple of the median. The acid-base status at birth as determined by arterial and venous umbilical cord blood pH was compared between weight-centile groups with and without low CPR. Results: CPR was better correlated with umbilical cord blood pH (arterial pH, r2 = 0.008, P < 0.0001 and venous pH, r2 = 0.01, P < 0.0001) than was birth weight (arterial pH, r2 = 0.001, P =0.180 and venous pH, r2 = 0.005, P < 0.001). AGA fetuses with low CPR were more acidemic than were those with normal CPR ( P = 0.0359 and 0.0006, respectively, for arterial and venous pH). Conclusions: The findings of this study demonstrate that low CPR in AGA fetuses is an equally important marker of low neonatal pH secondary to placental underperfusion as is being SGA. Although the relative importance of low CPR and birth weight in identifying pregnancies at risk of placental hypoxemia and adverse fetal and neonatal outcome remains to be determined, this finding may be of particular value in the prediction and prevention of stillbirth and long-term neurodevelopmental disability.