Acute hydramnios in the second trimester of pregnancy associated with twin to twin transfusion is a rare and usually disastrous complication. Few infants survive the neonatal period. We report a case of acute hydramnios prior to 20 weeks of gestation secondary to twin to twin transfusion documented by fetal blood samples obtained using cordocentesis. Selective fetacide was performed using a new procedure after a pericardial effusion had failed. The hydramnios resolved and the surviving co-twin was delivered at term.