To evaluate perinatal outcomes following fetoscopic laser placental photocoagulation (FLPC) performed for twin-to-twin transfusion syndrome (TTTS) at 16 weeks’ gestation (16.0 – 16.9 weeks), as compared to FLPC performed at 17 weeks’ gestation and beyond. This retrospective review included monochorionic twins complicated by TTTS necessitating FLPC at a single tertiary center from 2012 to 2021, with cohorts defined as cases undergoing FLPC at 16.0 to 16.9 weeks (early laser group) and cases with FLPC at 17 weeks or greater (standard laser group). Primary outcomes included rates of immediate chorioamniotic membrane separation (CAS), preterm premature rupture of membranes (PPROM), and chorioamnionitis. Primary outcomes were compared between cohorts, with a p-value of < 0.05 denoting statistical significance. Secondary outcomes included dual twin survival rates at birth and 30 days of life, adjusting for maternal age and Quintero stage at the time of FLPC. A total of 343 cases were included (35 early laser, 308 standard laser), with demographics summarized in Table 1. As seen in Table 2, the early laser group had significantly higher rates of CAS when compared to the standard laser group [34.3% vs 13.3% of cases (p < 0.001)]. The early laser group also demonstrated higher rates of PPROM [45.7% versus 25.0% (p=0.009)] and chorioamnionitis [11.4% vs 1.3% (p=0.005)]. Cessation of amniotic fluid leakage following PPROM occurred more frequently in the early laser group [37.5% vs 3.9% (p=0.001)]. Dual twin survival differed between the early and standard groups, although not significantly so. Early FLPC for TTTS performed at 16 weeks is associated with significantly higher rates of CAS, PPROM, and chorioamnionitis. However, amniotic fluid leakage tends to stop after PPROM following early FLPC, which we speculate may help to ameliorate some adverse fetal effects. Even after adjustment for higher Quintero staging in the early laser group, twin survival does not seem to be affected.View Large Image Figure ViewerDownload Hi-res image Download (PPT)