Thoracoamniotic shunting in fetal pleural effusion has poor results, with an overall survival of less than 50% when hydrops is associated. Those cases without hydrops presented the best evolution, but the indication in these cases remains controversial. We present a dichorionic diamniotic twin pregnancy at 29 weeks’ with right pleural effusion and hydrops, in which one fetus presented diaphragm inversion and mediastinal shift, both considered as ultrasonographic signs of thoracic hypertension. A thoracoamniotic shunt reversed these signs immediately. Nevertheless, 1 week after, these signs and skin edema reappeared and the effusion increased, leading to a second thoracocenthesis for drainage and intrathoracic pressure measurement. Amniotic fluid and intrathoracic pressures were found at 21 and 39 mm Hg, respectively. A cesarean section was performed and the catheter was found to be obliterated by cellular detritus of leukocytes and fibrin. Our conclusion is that ultrasonographic signs of elevated thoracic pressure are a keystone for the shunt indication, and that this could be corroborated by direct measurements. This can be an important parameter for precise indication of thoracoamniotic shunting.