(759) Intra-amniotic pressure changes during fetoscopic laser photocoagulation for twin-twin transfusion syndrome.

Objective:
To describe intra-amniotic pressure (IAP) changes during fetoscopic laser photocoagulation (FLP) and amnioreduction (AR) in pregnancies complicated by twin-twin transfusion syndrome (TTTS).

Study Design:
This was a retrospective analysis of monochorionic diamniotic twin pregnancies complicated by TTTS who underwent FLP and AR at our center between May 2024 and July 2025. We obtained IAP in mmHg before and after FLP and AR using a pressure-gauge transducer (TruWave, Edwards Lifesciences Corp.) connected to the fetoscopic port. We estimated median and interquartile ranges (IQR) for opening and closing IAP. Paired t-test assessed differences between the opening and closing IAP. Spearman rho (ρ) assessed the correlation between the amount of amniotic fluid volume removed and the difference between the opening and closing IAP.

Results:
Seventeen patients were included. The opening and closing IAP were 25.0 (20.0-31.5) and 20.5 (17.5-26.0) mmHg, respectively. There was a 5.2 mmHg drop in IAP following FLP and AR (p < .001). The net volume of amniotic fluid removed was moderately correlated with the change in IAP (ρ = 0.515, p = 0.04) (Figure 1).

Conclusion:
IAP decreases in pregnancies complicated by TTTS following FLP and AR. The higher the amount of amniotic fluid volume removed, the greater the degree to which the IAP drops. Larger studies are needed to validate our results and explore the relationship between changes in IAP during FLP and pregnancy outcomes.