The system is divided into five stages, each indicating the progression of the disease and the severity of the symptoms:
Stage I: The donor twin has oligohydramnios (decreased amniotic fluid) and the recipient twin has polyhydramnios (excessive amniotic fluid), but both twins have normal bladder filling and Doppler studies. Stage II: The donor twin's bladder is no longer visible, indicating severe oligohydramnios, while the recipient twin continues to exhibit polyhydramnios. Stage III: Abnormal Doppler studies are observed, including absent or reversed end-diastolic flow in the umbilical artery, reverse flow in the ductus venosus, or pulsatile flow in the umbilical vein. Stage IV: One or both twins show signs of hydrops fetalis, a condition characterized by severe fluid accumulation in at least two fetal compartments. Stage V: This is the most severe stage, where one or both twins have died.
