Association of preoperative uterine artery Doppler with persistent intertwin size discordance in twin–twin transfusion syndrome treated with fetoscopic laser surgery

OBJECTIVE: To determine the influence of preoperative uterine artery (UtA) Doppler abnormalities on disease severity, intertwin fetal-size discordance and perinatal outcomes in cases of twin-twin transfusion syndrome (TTTS) treated with fetoscopic laser surgery. METHODS: percentile and/or UtA notching. The primary outcome was the distribution of UtA Doppler abnormalities across TTTS stages. Secondary outcomes included the relationship between UtA Doppler findings and survival, gestational age at intervention, intertwin fetal-size discordance and intertwin birth-weight discordance. Analyses included non-parametric tests and regression models to identify predictors of intertwin size discordance. RESULTS: Of 509 treated cases, 378 pregnancies were included. Abnormal UtA Doppler occurred in 23.5% of pregnancies and was most frequent in those with Stage-III TTTS (32.4%; P = 0.004). Abnormal UtA Doppler findings were associated with lower maternal age, Stage-III TTTS and greater intertwin size discordance. Patients with UtA Doppler abnormalities had earlier laser surgery (median, 18.4 vs 19.4 weeks; P = 0.008) and exhibited greater prelaser intertwin fetal-size discordance (median, 23.9% vs 18.9%; P = 0.012), with higher proportions of intertwin discordance ≥ 25% before laser surgery (49.4% vs 33.2%; P = 0.006) and at birth (28.4% vs 13.9%; P = 0.004) compared to those without abnormal UtA Doppler. However, immediate post-laser survival and overall perinatal survival did not differ by UtA Doppler status. Multivariable linear regression analysis identified umbilical artery Doppler parameters as the primary determinant of intertwin size discordance, while abnormal UtA Doppler remained independently associated with intertwin size discordance both at the time of laser surgery and at birth. However, receiver-operating-characteristics-curve analysis showed that abnormal mean UtA-PI Z-score alone did not predict intertwin birth-weight discordance of ≥ 25%. CONCLUSIONS: Abnormal preoperative UtA Doppler was not a principal determinant of TTTS severity, but was most frequent in Stage-III TTTS. Abnormal UtA Doppler was associated with intertwin fetal-size discordance before laser treatment, with discordance persisting at birth despite successful surgery. Although abnormal UtA Doppler was independently associated with intertwin fetal-size discordance, elevated mean UtA-PI was not a clinically useful independent predictor of intertwin size discordance at birth. UtA Doppler and umbilical artery Doppler may be complementary in predicting fetal growth effects of placental dysfunction, independent of the acute cardiovascular effects of TTTS. © 2026 International Society of Ultrasound in Obstetrics and Gynecology.