Introduction
Monochorionic(MC) multiple pregnancies especially twin pregnancies, may be complicated by specific and serious complications, such as selective intrauterine growth restriction(sIUGR), twin-twin transfusion syndrome(TTTS), twin reversed arterial perfusion(TRAP), discordance for structural anomalies and twin anemia polycythemia sequence(TAPS). Untreated complicated MC multiple pregnancies disease may result in higher perinatal morbidity and mortality1.It is still controversial about whether selective reduction or laser ablation of  placental anastomoses is preferred for MC twins complicated with sIUGR or TAPS, while fetoscopic laser ablation was recognized as first-line treatment for stage Ⅱ to Ⅳ TTTs diagnosed before 26 weeks gestational age1. However ,in some situation, selective reduction is not a bad option due to few hospitals can perform laser ablation but fetal intrauterine condition are critical, especially in our country. Moreover, it can save one of the twin with a low risk of neurodevelopment impairment2.
During the recent years, radio frequency ablation has been widely used in many clinical therapies, such as neoplasm ,some heart disease3, human liver lesion, fetal congenital cystic adenomatoid (CCAM) 4, human fetal sacrococcygeal teratoma 5, and complicated monochorionic twin pregnancies 6, 7.While, it seemed that RFA is more minimal invasive to fetus and pregnant women than other methods for selective reduction used in multiple pregnancies. RFA was the most common technique for monochorionic multiple pregnancies selective reduction8.
The inserted angle is one of key points in the procedure of RFA. Usually, the procedure was conducted under direct real-time sonographic guidance, RFA needle was percutaneously inserted through the maternal abdomen wall into the intrauterine fetal abdomen at the level of the cord insertion site of the complicated twin7. However, fetus were positioned prone and remained throughout the whole procedure. Fetal back may can be alternative needle insert angle. However, the needle needs to pass through fetal spine which may obviously increases the difficulty and extended the procedure time of RFA. We hypothesis that the prenatal and postpartum outcome were worse in the cases through fetal dorsal insert angle.
In our study, the aim was to assess the risk factors for adverse pregnancy outcome in the RFA selective reduction procedure due to the complicated MC twin pregnancies and to compare the pregnancy outcome of two different needle insert angles in the RFA procedure.