Author responseVeronica Giorgione1, *Basky Thilaganathan1,2, Alessandra Familiari3,4, Elisa Bevilacqua31. Fetal Medicine Unit, St George’s University Hospitals NHS Foundation Trust, London, UK.2. Vascular Biology Research Centre, Molecular and Clinical Sciences Research Institute, St George’s University of London, London, UK.3. Department of Women and Child Health, Women Health Area, Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Rome, Italy.4. Catholic University of the Sacred Heart, Rome, Italy.*basky@pobox.comDear Professor Papageorghiou,We thank Prof. Wright and colleagues for their thoughtful comments on our paper “Predicting Adverse Perinatal Outcomes in Dichorionic Twin Pregnancies” .1 We welcome the opportunity to clarify the issue of ultrasound timing and to present additional sensitivity analyses addressing their concerns.As noted by the authors, in our study estimated fetal weight (EFW) and Doppler measurements were obtained within two weeks of delivery or an adverse fetal event. This approach reflects standard clinical practice in twin pregnancy, where surveillance is intensified when fetal compromise is suspected. As detailed in the Methods, our aim was to build an antenatal prediction model using routinely collected variables rather than to investigate causal pathways leading to delivery. Importantly, all ultrasound assessments were performed within two weeks of the outcome of interest, and therefore the timing of scans does not invalidate the associations, but does influence how the model is used clinically.We feel it is important to re-iterate that the primary outcome of the study was stillbirth at any gestation or indicated birth before 34 weeks’ gestation for concerns over fetal wellbeing. As such, we included data from scans beyond 34 weeks in the original analysis because the majority of pregnancies progressed beyond this gestation regardless of whether they subsequently resulted in a livebirth or were stillborn.Nevertheless, to address the potential temporal overlap highlighted by Wright and Nicolaides, we performed a dedicated sensitivity analysis restricted to pregnancies in which the index scan occurred before 34 weeks’ gestation, which comprised 333 dichorionic twin pregnancies. The model combining EFW and umbilical artery (UA) pulsatility index discordance achieved an AUC of 0.87 (95% CI 0.81–0.93), with odds ratios of 1.06 (95% CI 1.03–1.08) and 1.06 (95% CI 1.04–1.08), respectively. Adding middle cerebral artery (MCA) Doppler or SGA 0.86–0.89). These results confirm that the predictive ability of fetal biometry and Doppler discordance remains robust when analyses are limited to measurements obtained entirely before the 34-week threshold.We acknowledge that, as in any observational study, ultrasound scheduling and clinical decisions may introduce elements of interventional bias. However, by restricting analyses only to ultrasound data collected at least two weeks before delivery or an adverse outcome, and confirming comparable performance in the <34 week subset, we believe the influence of such bias on our estimates is minimal. Future prospective studies with standardised scanning intervals could further validate these findings.In conclusion, our sensitivity analysis demonstrates that EFW and UA PI discordance measured before 34 weeks maintain high predictive accuracy for stillbirth or iatrogenic preterm birth <34 weeks, underscoring the robustness and clinical applicability of our model. We thank Prof. Wright and colleagues for prompting this clarification, which we believe strengthens the evidence base for antenatal risk stratification in dichorionic twin pregnancies.Sincerely,Veronica Giorgione, on behalf of all authors1. V Giorgione, M Trapani, M Lopian et al., “Predicting Adverse Perinatal Outcomes in Dichorionic Twin Pregnancies: A Multicentre Cohort Study” British Journal of Obstetrics and Gynaecology. 2025 Jun;132(7):983-990.
