(742) Microwave ablation for selective fetal reduction in complicated monochorionic gestations

Second trimester selective fetal reduction (SFR) in monochorionic (MC) gestations has a cotwin loss rate of 18-40%.  Microwave ablation (MA) is a newer technique for SFR with minimal thermal spread and a precise area of coagulation along the end of the needle and may result in lower preterm birth rates. We aimed to evaluate MA for SFR in MC gestations.

Study Design:

The surgical technique for MA is similar radiofrequency ablation. A 16-gauge microwave antennae is utilized under ultrasound guidance. Coagulation, tissue contact, and temperature are monitored.  Demographics, procedure details and outcomes were evaluated for patients who underwent MA for SFR from 11/2017 to 4/2023 with available delivery outcomes. Our primary outcome was co-twin survival. Secondary outcomes included gestational age (GA) at delivery and procedure to delivery interval. Continuous data were analyzed using Student’s t-tests or Wilcoxon Rank Sum test. Categorical data were analyzed using Chi-square tests or Fisher’s Exact.

Results:

Of 27 patients, 25 were MC twins, 1 was MC triplets and 1 was dichorionic triplets. MA was performed for twin reversed arterial perfusion in 14 (52%), discordant anomalies in 9 (33%), and twin to twin transfusion or selective fetal growth restriction in 6 (22%). Co-twin survival was 85%. Cotwin losses were due to previable birth (n=1), post operative intraventricular hemorrhage (n=1), septostomy with t cord entanglement (n=1), and post op day 1 demise (n=1). GA at delivery for 23 ongoing and delivered pregnancies was 37.7 [34-.1 - 38.9] weeks and interval to delivery was 17.2 [13.8 – 19.7] weeks. Between surviving and demised co-twins there was no difference in BMI, race, cervical length, gestational age, twin weight ratio, procedure time, or procedure energy. Transplacental entry was more frequent in co-twin demise (3/4 vs 5/23, p=0.03).

Conclusion:

MA is a newer technique for SFR in MC twins thus far demonstrating favorable outcomes.  Transplacental entry may be a risk factor for cotwin demise. Further studies are needed to evaluate outcomes and refine the technique.