Objective: We aimed to investigate the incidence, prenatal factors, and outcomes of twin-to-twin transfusion (TTTS) with right ventricular outflow tract obstruction (RVOTO). Search Strategy: A systematic search was conducted to identify relevant studies published until February 2023 in English using the databases PubMed, Scopus, and Web of Science Selection Criteria: Studies reporting on pregnancies with TTTS and RVOTO were included. Primary outcome was survival including fetal demise, neonatal death, and 6-months survival. Secondary outcomes were incidence and prenatal risk factors. Data Collection and Analysis. The random-effect model pooled the mean differences or odds ratios (OR) and the corresponding 95% confidence intervals. Heterogeneity was assessed using the I2 value. Results: 17 studies encompassing 4332 TTTS pregnancies of which 225 cases had RVOTO were included. Incidence of RVOTO at time of TTTS diagnosis was 6%. 134/197 (68%) had functional pulmonary stenosis (PS) and 62/197 (32%) had functional pulmonary atresia (PA). 27% resolved following laser and 55% persisted after birth. Of those persisting, 27% required cardiac valve procedures. Risk factors were TTTS stage III (53% vs 39% in no-RVOTO), stage IV TTTS (28% in RVOTO vs 12% in no-RVOTO), and DV reversed a-wave (60% in RVOTO vs 19% in no-RVOTO). GA at laser and GA at delivery were comparable between groups. Survival outcomes were also comparable between groups including fetal demise of 26%, neonatal death of 12%, and 6-months survival of 82% in RVOTO group. Findings were similar when subgroup analysis was done for studies including head-to-head analysis. Conclusions: RVOT occurs in about 6% of the recipient twins with TTTS, especially in stages III and IV and those with reversed DV a-wave. The findings from this systematic review support the need of a thorough cardiac assessment of pregnancies complicated by TTTS, both before and after laser in order to maximize perinatal outcome and the importance of early diagnosis of TTTS and timely management. Tweetable abstract: Meta-analysis shows that the incidence of right ventricular outflow tract obstruction among TTTS pregnancies is 6%, among which 68% had functional pulmonary stenosis and 32% had functional pulmonary atresia. Of these pregnancies, 27% resolved after laser therapy and 55% persisted after birth. Of cases persisting after birth, 27% required cardiac valve procedures. Significant risk factors were TTTS stage III-IV and ductus venosus a-wave reversal. Survival outcomes including fetal demise, neonatal death, and 6-months survival were similar compared to those without RVOTO.
