Co‐Occurrence of Osteogenesis Imperfecta Type <scp>III</scp> and Chronic Abruption‐Oligohydramnios Sequence: A Case Report Suggesting a Possible Role of Type I Collagen Fragility

Pregnancy complicated by severe osteogenesis imperfecta (OI) is rare, and chronic abruption-oligohydramnios sequence (CAOS) is an uncommon obstetric disorder characterized by persistent bleeding and oligohydramnios without membrane rupture. To our knowledge, this is the first report describing the coexistence of type III OI and CAOS. A 24-year-old woman with OI developed recurrent bleeding early in pregnancy. Genetic testing revealed a novel COL1A1 splice-site variant (c.1876-2A>C). Ultrasonography showed a circumferential subchorionic hematoma and progressive fluid loss, leading to CAOS diagnosis at 19 weeks. Despite amnioinfusion, the amniotic cavity collapsed, and pregnancy was terminated via cesarean section at 20 weeks. Placental pathology showed hemosiderin and fibrin deposition. In this case, both functional and structural factors possibly associated with type I collagen abnormalities may have contributed to CAOS development. Although causality cannot be proven, persistent bleeding in severe OI may warrant greater caution for progression to CAOS.