We thank these authors for their interest in our paper.

We are indeed proposing to examine whether pH adds to the predictive value of base deficit, and this analysis is planned.

We are unclear whether there is evidence to support the authors’ contention that a respiratory acidosis, which is obviously extremely uncommon in the fetus, does not lead to cellular damage.

Many authors, including us and those of the letter, have previously demonstrated how poorly cord gases correlate with neonatal outcomes, whatever measures are used. Some of this is because the pH in the cord is not always the same because the pH in every area of the head because of the variable mechanisms of intrapartum fetal compromise. We urgently need a better marker of intrapartum cellular compromise.