We thank Dr Morales-Roselló et al for their interest in the PORTO study and would like to respond to some of their comments that relate to our recent publication on the role of brain-sparing in the setting of fetal growth restriction (FGR).

We entirely agree with Dr Morales-Roselló et al that FGR is not a single disorder; this is precisely the reason that the Prospective Observational Trial to Optimize Pediatric Health in IUGR (PORTO) “lumped all FGR cases together” (excluding structurally and genetically abnormal fetuses). Undoubtedly, FGR presents clinicians with a complex situation whereby the exact cause unfortunately often is not known until after delivery. This is the reason that we also believe that the situation in prenatally identified FGR is more difficult than simply “2 different diseases”: early and late FGR.

Of the 418 fetuses with abnormal umbilical artery (UA) Doppler imaging, 128 fetuses (31%) presented an abnormal cerebroplacental ratio (CPR). In those fetuses with normal UA, just 18 (3%) had an abnormal CPR. In other words, 88% (128/146 fetuses) of those with abnormal CPR also had an abnormal UA assessment. This indicates that the population of those fetuses with abnormal CPR was very much contained within the population of those who had an abnormal UA Doppler image. The mean gestational age for abnormal CPR in the PORTO cohort was 32 weeks, which was similar to the onset of abnormal UA (also 32 weeks). Abnormal CPR that occurred at <34 weeks’ gestation vs >34 weeks’ gestation was presented in Table 2.

As outlined in our article, it was difficult to interpret whether the CPR calculation is more predictive at <34 weeks’ gestation, given the small number of adverse outcomes beyond this gestation. This is possibly related to the fact that many fetuses were delivered before changes in their CPR. We look forward to reading the forthcoming publication on the correlation between CPR and acid base status in term fetuses.