Abstract： Objective:To investigate the prenatal genetic features and the factors influencing the prognosis of twin reversed arterial perfusion sequence (TRAPS) in monochorionic twin pregnancies.Methods:A total of 99 cases diagnosed with TRAPS by prenatal ultrasound in the First Affiliated Hospital of Sun Yat-sen University from July 1, 2007, to December 31, 2021, were included retrospectively. The prenatal genetic features of acardiac and pump twins were analyzed. Eighty-nine cases were followed up and divided into two groups: the expectation group ( n=45) and the intrauterine intervention group (all underwent radiofrequency ablation, n=44) and the pregnancy outcomes were compared between the two groups. After excluding eight cases without complete ultrasound data, the expectation group was further divided into two subgroups: the pump fetus survival ( n=28) and the pump fetus death groups ( n=9), and the survival subgroup was divided into the spontaneous arrest group ( n=16) and coexistence group ( n=12) according to whether or not the blood flow stopped spontaneously.The relationship between ultrasonic indexes and pregnancy outcome was compared between the groups. Chi-square test (or Fisher's exact test), univariate logistic regression analysis and receiver operating characteristic (ROC) curve were used to analyze the relationship between the estimated acardiac to pump twin weight ratio (A/P Wt) and the pregnancy outcome of the pump twin in the expectation group. Results:(1) The median gestational age at diagnosis of the 99 TRAPS cases was 16.4 weeks (13.3- 21.3 weeks) and 32% (32/99) were diagnosed in the first trimester. Most of the cases were monochorionic diamniotic pregnancies (72/99, 73%). The survival rate of the pump twins was 71% (63/89). (2) Chromosome karyotyping and/or chromosomal microarray analysis was performed in 19 acardiac twins and 82 pump twins. The detection rate of genetic abnormalities in the acardiac twins was higher than that in the pump twins [4/19 vs 5% (4/82), Fisher's exact test, P=0.039]. Chromosomal microarray analysis was performed in 54 pump twins with normal karyotypes and the results showed three (6%) with genetic abnormalities. (3) In the expectation group, the area under ROC curve for the prenatal A/P Wt were 0.913 in predicting pump twin death and 0.807 in predicting spontaneous cessation of blood flow in the cardiac twin, and the cut-off values were 0.24 (sensitivity: 88.9%, specificity: 96.4%) and 0.11 (sensitivity: 75.0%, specificity: 81.3%), respectively. The survival rate of pump twins with abnormal cardiac function after intrauterine intervention was higher than that of the expectant group [72% (18/25) vs 3/11, Fisher's exact test, P=0.025]. Conclusions:TRAPS can be diagnosed in the first trimester and commonly occur in monochorionic diamniotic pregnancies. The detection rate of genetic abnormalities in the acardiac twins is higher than that in the pump twins. Prenatal A/P Wt>0.24 indicates the death of the pump twin and prenatal A/P Wt≤0.11 suggests a high possibility of spontaneous cessation of blood flow in the acardiac twin. Radiofrequency ablation is an effective method for improving the prognosis of the pump twin with cardiac dysfunction.