Chronic abruption-oligohydramnios sequence (CAOS), characterized by chronic vaginal bleeding and oligohydramnios, is associated with adverse pregnancy outcomes, including preterm delivery and lung problems in the infant. Fetal lung damage may be induced by not only oligohydramnios but also iron-induced oxidative stress through chronic aspiration of bloody substances in amniotic fluid. We describe a pregnancy complicated with CAOS that was managed with repeated amnioinfusions. This is the first report showing that amnioinfusions succeeded in a significant reduction in high concentrations of iron, lactose dehydrogenase, and 8-hydroxy-2'-deoxyguanosine, a marker of oxidative DNA damage, in the amniotic fluid complicated by CAOS. The baby, born at 26 weeks' gestation via cesarean, was discharged home without supplemental oxygen 116 days after birth.