Differential Diagnosis for Sudden Gush of Bright Red Blood During Labor

• Single most likely diagnosis:
  • Placenta praevia: This condition is characterized by the placenta partially or completely covering the internal cervical os, which can cause painless, bright red vaginal bleeding, especially after rupture of membranes (AROM). The sudden gush of bright red blood following AROM and the subsequent fetal distress (indicated by a drop in FHR to 75 bpm) are highly suggestive of placenta praevia.
• Other Likely diagnoses:
  • Vasa praevia: This condition involves fetal blood vessels running through the membranes over the internal cervical os, unprotected by Wharton's jelly. Rupture of these vessels during AROM can lead to sudden, significant fetal blood loss and distress, presenting as a gush of bright red blood. The key distinguishing feature from placenta praevia is the source of the bleeding (fetal vs. maternal).
• Do Not Miss diagnoses:
  • Uterine rupture: Although less likely given the scenario (no previous uterine surgery is mentioned, and the patient is a primigravida), uterine rupture is a catastrophic event that can present with sudden fetal distress and maternal hemorrhage. It is crucial to consider this diagnosis, especially if there are risk factors not mentioned in the scenario.
• Rare diagnoses:
  • Bloody show: Bloody show is a small amount of blood or blood-tinged mucus that is expelled from the cervix as the body prepares for labor. It is typically not associated with a sudden gush of bright red blood or significant fetal distress, making it an unlikely diagnosis in this scenario.