Discussion
The aim of this study 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. We found that both needle insert angles were equal in terms of the fetal neonatal survival rate and the adverse perinatal outcomes of the monochorionic multiple pregnancies. Selective reduction due to the indication of TTTS accompanied with sIUGR was associated with more favorable pregnancy outcome, regardless of the procedure technique. There was similar survival rate in those whom selective reduction was performed through fetal dorsal insert angle by comparison with abdominal insert angle. Even though there was no significant difference, the survival rate was lower in patients in whom RFA procedure was performed at a pre-viability gestational age in comparison to post-viability.
Usually, the radio frequency needle was inserted percutaneously into fetal abdomen to the intra-fetal portion of umbilical cord7, 11. Our study found that when the fetus stay in prone position, the needle need to be inserted into fetal back and then the umbrella Electrode were deployed, electrical energy was transferred to fetal tissue with heat as usual insert angle, needle abdominal insertion 3, 7, 12. In our series, technique success was obtained in all cases by inserting the needle once in both groups, abdominal and dorsal needle insert angle.
Previous studies have explored the pregnancy outcome of selective reduction in complicated monochorionic multiple pregnancies as a function of the technique used2, 13, 14, especially in complicated MC twin pregnancies. Our research showed similar perinatal survival rates and adverse perinatal outcome rates for both needle insertion. The overall survival rate was 73.4% and the overall gestational age at labor was 31.09±6.04 weeks. Even though there was no significant difference between the two groups, our finding indicated a trend towards earlier gestational age among the needle dorsal insertion group(one week earlier than the needle abdominal insertion). Such a difference in gestational age at delivery may be clinically significant in terms of the adverse perinatal outcome, such as neonatal morbidity and mortality.
In respect of the effect of the indications of RFA selective reduction on the perinatal outcome, we found that TTTS accompanied with sIUGR was associated with a predominant outcome with a survival rate of more than 90%, obviously higher than other studies15. A probable explanation was that in the cases suffered TTTS accompanied with sIUGR, the smaller twin present a obvious disadvantage status due to the uneven placental share16 and imbalance of placental arteriovenous anastomosis17, after fetal reduction, the intrauterine environment of the co-twin was closer to a singleton pregnancy than other indications.
It is well known that cervical length can be a good predictor of spontaneous preterm birth in asymptomatic twin pregnancy18. Our study found that the survival curve of fetal survival time interval after the procedure between the two needle insert angles were statistically different(P <0.001), with two significant predictors, cervical length (RR=0.969, P =0.043) and the gestational age before the procedure (RR=1.205, P <0.001) . Moreover, multivariable logistic analysis showed that compared to live birth at term, the risk of miscarriage,termination and IUFD were statistically higher when the cervical length was less than 35mm. Therefore, we recommend that cervical length and gestational age should be attentively evaluated before the clinical decision making about RFA selective reduction.
The preterm delivery outcomes were chosen due to their clinical importance. Neonates delivered prior to 28 weeks gestational age were acknowledged as “extremely preterm” and have a significantly lower survival rate compared to “very preterm”(28-32 weeks) and “moderate to late preterm” (32-36 weeks) neonates19. Gestational age specific survive curve showed a significant improvement with delivery later than 32 weeks gestational age across the world20, 21. In our study, the overall rate of preterm delivered before 32 weeks gestational age within the indication was lower than some research but higher than someones22, 23, this may due to the severity of the disease or cervical length or gestational age or other reasons.
The main limitations of this study are its retrospective study design and short follow-up time, which meant lack of the long-term follow-up outcome assessments of neurodevelopment of surviving fetuses. Second, our study was performed and followed at an fetal therapy center. Besides, after our team became more proficient and confident in the operation of selective fetal reduction, we began to perform fetal reduction with unconventional needle insertion angles such as dorsal side needle insertion. We will prospectively investigate the long-term follow-up outcomes of surviving fetuses with RFA procedure at two different needle insertion angles.