We present an unusual case of TRAP sequence (twin reversed arterial perfusion) with persistent polyhydramnios despite spontaneous thrombosis of the vena umbilicalis of the acardius. Serial amnioreduction was performed owing to considerable maternal discomfort and preterm labor. After three procedures, spontaneous abortion occurred. Unexpectedly, the normal twin had an apparently recent constriction of the right forearm. We hypothesize that limb constriction could be a rare but specific complication of aggressive amnioreduction.