Editor—Gupta et al 1 have successfully demonstrated that they were unable to accurately predict PaO ₂ from saturation monitoring even after standardising from a previous measurement. The rest of the conclusions presented in their discussion are however based upon interpretation of other research findings which is not further supported by their own study.

They correctly point out that the poor relation between SpO ₂ and PaO ₂ is related to differing proportions of fetal haemoglobin, Pco ₂, and acid–base balance. This begs a question, which their discussion fails to address, on whether the PaO ₂ or the SpO₂ is the most useful index of oxygenation. It is certainly the case that normal in utero PO ₂ is within a range which they would describe as “hypoxic”. On the other hand, in the presence of …