Development and external validation of prognostic markers to predict pump-twin survival in twin reversed arterial...

To evaluate the outcome of monochorionic diamniotic (MCDA) pregnancies complicated by twin reversed arterial perfusion (TRAP) sequence and to evaluate potential prognostic ultrasound markers as predictors of pump-twin survival.

This was a retrospective cohort study of MCDA twin pregnancies diagnosed with TRAP sequence at two medical centers in China between January 2010 and December 2024. All cases were analyzed retrospectively for intrauterine course and outcome. Cases that underwent expectant management were assigned to the primary cohort (cases from the First Affiliated Hospital of Sun Yat-sen University, Guangzhou) or the external-validation cohort (cases from Dalian Women and Children's Medical Group, Dalian). Cases that underwent intrauterine intervention at the First Affiliated Hospital of Sun Yat-sen University were assigned to the intrauterine-intervention cohort. The following parameters were evaluated in the primary and external-validation cohorts for their predictive value regarding pump-twin survival: in the first trimester, the crown-rump length (CRL) and nuchal translucency thickness of the pump twin, the upper pole-rump length (URL) of the acardiac twin, the URL/CRL ratio, and the presence of reversed a-wave in the ductus venosus and the umbilical artery pulsatility index (UA-PI) in the acardiac twin; and in the second trimester, the URL of the acardiac twin, the estimated fetal weight (EFW) of each twin, the twin weight ratio (TWR) (EFW_{acardiac twin}/EFW_{pump twin}) and the UA-PI of each twin. Univariate Cox regression analysis was performed to identify the parameters associated with pump-twin survival. Performance was evaluated by the area under the receiver-operating-characteristics curves (AUCs) and calibration curves. Finally, Kaplan-Meier survival analysis was performed.

A total of 117 MCDA pregnancies with TRAP sequence were included in the analysis: 55 in the primary cohort, 38 in the intrauterine-intervention cohort and 24 in the external-validation cohort. The overall pump-twin survival rate was 65.8% (77/117). Three variables (URL and URL/CRL ratio in the first trimester and TWR in the second trimester) were identified to be independent risk factors influencing pump-twin survival in both the primary and external-validation cohorts. The AUCs were indicative of good predictive discrimination in both cohorts: 0.811 (95% CI, 0.667-0.956) for URL, 0.780 (95% CI, 0.619-0.941) for the URL/CRL ratio and 0.859 (95% CI, 0.730-0.988) for TWR in the primary cohort; and 0.844 (95% CI, 0.662-1.000) for URL, 0.823 (0.633-1.000) for the URL/CRL ratio and 0.925 (95% CI, 0.766-1.000) for TWR in the external-validation cohort. The optimal cut-off values were 4.85 cm for URL, 0.54 for the URL/CRL ratio and 0.295 for TWR in the primary cohort. The TWR exhibited good calibration, but URL and the URL/CRL ratio exhibited poor calibration. Kaplan-Meier survival analysis revealed that pump twins with TWR ≥ 0.295 experienced a significantly shorter intrauterine survival duration in both the primary and external-validation cohorts, and pump twins with URL ≥ 4.85 cm or URL/CRL ratio ≥ 0.54 experienced a significantly shorter intrauterine survival duration in the primary cohort. However, the optimal cut-offs of URL and the URL/CRL ratio showed no statistical difference in the external-validation cohort.

After 14 + 0 weeks' gestation, the threshold of TWR < 0.295 can reliably predict survival of the pump twin in MCDA pregnancies with TRAP sequence. However, the predictive value of URL and the URL/CRL ratio in the first trimester for pump-twin survival is poor. A well-designed prospective multicenter study is warranted to develop a first-trimester multivariable predictive model with enhanced predictive performance. © 2026 International Society of Ultrasound in Obstetrics and Gynecology.