We thank Dr Ferrazzi for his interest in the Prospective Observational Trial to Optimize Pediatric Health in IUGR (PORTO) study and would like to respond to his comment regarding the gestational age perspective of Doppler interrogation of intrauterine growth-restricted (IUGR) fetuses.

We acknowledge the mentioned limitations of our study, namely that not all fetuses enrolled in PORTO had abnormal umbilical artery Doppler studies, the later gestational age at delivery for the overall cohort, and the lack of prespecified delivery indicators. PORTO did not claim to be an interventional study. Its prospective observational design, however, afforded the opportunity to study a large cohort of fetuses with estimated fetal weight at <10th percentile, which gave valuable insight into prenatal events and clinicians’ decision-making processes. We wish to clarify that the Trial of Umbilical and Fetal Flow in Europe enrolled singleton fetuses between 26 and 32 weeks gestation with abdominal circumference <10th percentile and umbilical artery pulsatility indices >95th percentile, irrespective of uterine artery Doppler findings.

PORTO documented the sequence of Doppler events on an individual fetal patient level over time rather than presenting cumulative abnormalities within a defined cohort. We found that there simply was no single predominant Doppler pathway; undoubtedly, this observation came as a bit of a surprise to us, given the previous presumption that IUGR followed a predictable progressive deterioration in utero. In addition, we evaluated longitudinal changes in a subgroup of fetuses with EFW <3rd percentile and those who required delivery at <34 weeks’ gestation, which attested to the severity of IUGR that did not differ from patterns in the overall cohort. PORTO was not simply a study of late onset IUGR; we had a significant proportion of severe early-onset IUGR cases, and our conclusions were similar among both early- and late-onset cases.

We certainly do not dismiss the research efforts that have gone into the longitudinal Doppler evaluation with the aim of understanding the underlying pathophysiologic condition, optimizing surveillance strategies, and guiding the optimal timing of delivery. However, it is a common misconception among readers of previous studies of Doppler events in the setting of IUGR that the accumulated data refer to a pattern of deterioration in individual fetuses; this is not the case. Our data highlight the complexity and often unpredictability of Doppler deterioration in the IUGR setting. In fact, many publications in this field acknowledge the large variability in manifestation of Doppler abnormalities that occur in IUGR with only a minority of fetuses exhibiting 1 single predominant pathway.