Abstract
Objective
To invent a novel method for selective fetal reduction in monochorionic (MC) twin using cool-tip radiofrequency ablation (RFA) and analysis the perinatal outcome.
Material and methods
Complicated MC twins including twin-to twin transfusion syndrome (TTTS), selective fetal growth restriction (sFGR) and twin reverse arterial perfusion sequence (TRAP) were enrolled from 2020 to 2024. All cases were indicated for selective fetal reduction due to expected poor outcome. Equilateral triangle method using single puncture 4 times ablation with 17G cool-tip RFA to cord insertion site, umbilical vein and two umbilical arteries for complete stopping the blood flow. The power was starting from 60 W, 80 W, 80 W and 100 W 1 min each site. Outcome were analyzed.
Results
A total of 51 cases were collected and treated in a single medical center. We divided first 20 cases as tradition group using single point ablation and novel 4-point ablation group after 21st cases. The overall co-twin survival rate after RFA procedure was 88 % (45 out of 51) in whole series. However, the co-twin survival rate in the novel 4-point group was better than single point group (93.5 % vs 80 %) with statistically significance. The maternal age, procedure at gestational age, procedure time and preterm birth rate did not show statistically difference between two groups.
Conclusions
This novel equilateral triangle method to stop all the umbilical blood flow achieved the high successful rate without maternal complication. The 17 g cool-tip RFA worked at low temperature to avoid thermal damage. This might be the new choice of RFA in monochorionic pregnancies.
Introduction
Since 2009, the average maternal age in Taiwan has increased by approximately 1.99 years, with over 60 % of pregnancies now occurring in women aged 30–39. This rise in maternal age, coupled with the growing use of assisted reproductive technologies, has contributed to an increase in multiple births [ ]. Data from Taiwan’s Ministry of the Interior show that twins accounted for 2.3 % of births in 2000, rising to 4.1 % in 2021.
Monochorionic twin pregnancies, comprising 20 % of twin cases [ ], are associated with complications including twin–twin transfusion syndrome (TTTS), selective fetal growth restriction (sFGR), twin reversed arterial perfusion sequence (TRAPs), and twin anemia-polycythemia sequence (TAPS) [ ]. These complications arise from placental vascular anastomoses, leading to shared circulatory dynamics between fetuses [ ] and contributing to a perinatal mortality rate as high as 15 % [ ]. Furthermore, the loss of one fetus can result in inter-twin transfusion, increasing the risk of severe neurological impairment or death in the co-twin by 12–26 % [ , ]. In cases of severe monochorionic complications, selective fetal reduction (SFR) may be essential to enhance the remaining fetus’s survival rate [ ].
Selective fetal reduction can be achieved through several umbilical cord occlusion (UCO) techniques, including fetoscopic laser photocoagulation [ , , , ], fetoscopic cord ligation [ , ], bipolar cord coagulation (BCC) [ , ], and radiofrequency ablation (RFA) [ , , , , ]. Recent studies favor RFA over traditional laser photocoagulation due to simpler operative settings [ ] and better pregnancy outcomes [ , , , ]. However, determining the optimal energy source and intensity remains a subject of debate.
The Cool-Tip RFA system, commonly used in oncology for liver metastases [ ], employs hollow electrodes with internally circulating chilled water, allowing for precise thermal ablation with controlled cooling of adjacent tissue [ ]. M. Wagata et al. first applied this system in 22 TRAP cases in monochorionic twins, but further data on Cool-Tip RFA use in monochorionic pregnancies remain limited [ ]. We also invent a novel technique method to improve the clinical outcome. The Fetal Medicine Unit at Taipei Chang Gung Memorial Hospital is one of the few centers in East Asia supporting fetal therapy and pioneering Cool-Tip RFA use in Taiwan. This study shares our clinical experience and outcomes using Cool-Tip RFA in complicated monochorionic pregnancies.
Maternal and methods
Participants recruitment and selection
From 2020 to 2024, over 50 high-risk monochorionic pregnancies have been treated with RFA at the Fetal Unit of Taipei Chang Gung Memorial Hospital, all involving one abnormal and one healthy twin or MC triplet/quadruplets. Prior to the procedure, ultrasound assessments were conducted to evaluate placental positioning, abnormal growth or malformations, amniotic fluid volume, and umbilical artery blood flow, along with comprehensive counseling on potential perinatal morbidity risks. This study was approved by Chang Gung Medical Foundation Institutional Review Board (CGMF Ref. No. 202001436B0).
Equilateral triangle 4 points RFA technique
The procedures, performed under local anesthesia (lidocaine) in a sterile environment between 16 and 24 weeks’ gestation, used the Covidien E-Series ablation system with a 17-gauge Cool-tip radiofrequency ablation needle (1.4 mm in diameter). Under real-time ultrasound guidance, the Cool-Tip needle was inserted percutaneously through the maternal abdominal wall, reaching the targeting fetus’s umbilical cord insertion site. Then ablation was started to stop the blood flow. The whole setting was demonstrated in Fig. 1 . All cases were operated by S.W. Shaw.
We invented this Cool-Tip system’s 4-point ablation design deploys three electrodes in an equilateral triangle configuration, each directed at an umbilical vessel. Ablation points were positioned just below the fetal umbilicus, targeting the umbilical vein and two umbilical arteries. Thermal energy, at a target temperature of 80 °C, was delivered in cycles at increasing power levels (60 W, 80 W, 80 W, and 100 W), each lasting 1 min with a 20–30 s interval between cycles. The needle was not pulled out of the fetal body but only changing the angle around the umbilical vessels. After four cycles, blood flow in the abnormal twin ceased successfully ( Fig. 2 ). The first 20 cases were using the traditional method (one ablation point), then we started the 4-point method after 21st case. We invented the new RFA technique due to some failure cases with remaining vessels even after ablation. The remaining flow caused the death of co-twin. The new method could ensure all the blood flow was completed stopped to increase the successful rate. All the results will be compared between two groups.
Data collection
The following data were collected: maternal age, body mass index, parity, mode of conception (assisted reproductive technology or spontaneous), GA at RFA, indications for selective reduction, complete ablation time, overall survival rate, fetal loss within 2 weeks after RFA, preterm premature rupture of membranes (PPROM) within 2 weeks after RFA, GA at delivery, procedure-to-delivery interval, mode of delivery, neonatal death, birth weight of live neonate, admission to the neonatal intensive care unit (NICU), and need for mechanical ventilation. The comparison was demonstrated between two groups.
Statistical analysis
Statistical analysis was performed using IBM SPSS Statistics for Windows, Version 22.0. Categorical variables were compared using the Chi-square or Fisher exact test as appropriate. A p value (2-tailed) ≤0.05 was considered statistically significant.
Results
A total of 51 cases were collected since 2020 to 2024 and treated in a single medical center. We divided first 20 cases as traditional group using single point ablation and novel 4-point ablation group after 21st cases. Four out of first 20 cases were found co-twin death one day after the procedure. The main reason was incomplete ablation with remaining blood flow. In order to ensure all the blood flow (two umbilical arteries and one umbilical vein) was fully stopped, the new 4-point method showed the better outcome and higher successful rate compared to the traditional single point method.
The overall co-twin survival rate after RFA procedure was 88 % (45 out of 51) in whole series. However, the co-twin survival rate in the novel 4-point group was better than single point group (93.5 % vs 80 %) with statistically significance ( Table 1 ). The maternal age, procedure at gestational age, procedure time and preterm birth rate did not show statistically difference between two groups. The indication for RFA including sFGR or one co-twin anomaly, TTTS, TRAP or MC triplets/quadruplet also showed the distribution in the table.
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