The objective of this study was to evaluate the feasibility, efficacy and safety of bipolar coagulation using endoscopic forceps of diameters of 2.7 mm and less in animal models mimicking in-utero conditions. Forceps of 2.2, 2.3, 2.5 and 2.7 mm were tested in rabbits (n = 36). Vessel pairs were dissected and coagulated in a fluid environment under endoscopic vision at 15 and 25 W. The main outcome measure was the perforation rate. In fetal lambs (n = 25), umbilical cords were coagulated under sono-endoscopic control with power settings from 10 to 35 W. Main outcome measures were the duration of coagulation, perforation rate, change in the temperature of the amniotic fluid and efficacy of vessel occlusion rate. At 20-25 W, all cords were coagulated successfully without any perforation using 2.3, 2.5 or 2.7 mm forceps. Coagulation with the 2. 2 mm forceps was associated with a high perforation rate, although the design rather than the diameter of the forceps may have influenced this outcome. Bipolar coagulation with forceps between 2. 3 and 2.7 mm and appropriate power settings achieves efficacious and safe coagulation in animal models for umbilical cord occlusion.