Differential Diagnosis for 21-week Placenta Covering OS and Bleeding

• Single most likely diagnosis
  • Placenta Previa: This condition is characterized by the placenta partially or completely covering the internal cervical os, which can cause bleeding, especially in the second or third trimester. The presentation of placenta covering the os and bleeding at 21 weeks is highly suggestive of placenta previa.
• Other Likely diagnoses
  • Placental Abruption: Although more commonly associated with abdominal pain and bleeding, placental abruption can sometimes present with painless vaginal bleeding and should be considered, especially if there's a history of trauma or other risk factors.
  • Vasa Previa: This condition involves fetal blood vessels crossing the internal cervical os, which can cause bleeding when ruptured. It's less common than placenta previa but should be considered, especially if there's a history of uterine surgery or multiple gestations.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Uterine Rupture: Although rare, uterine rupture can present with sudden onset of abdominal pain and bleeding. It's a life-threatening emergency that requires immediate intervention.
  • Placenta Accreta Spectrum (PAS) Disorders: These disorders involve abnormal placental attachment and can cause severe bleeding. While often associated with placenta previa, they can occur independently and are critical to diagnose due to their potential for severe maternal morbidity.
• Rare diagnoses
  • Choriocarcinoma: A rare malignant tumor that can cause bleeding and is associated with pregnancy. It's much less common than other causes of bleeding in pregnancy but should be considered in the differential diagnosis, especially if other causes are ruled out.
  • Uterine Artery Aneurysm or Pseudoaneurysm: These vascular abnormalities can cause bleeding during pregnancy and, although rare, are important to consider due to their potential for severe hemorrhage.