Clinical meaning
Postpartum hemorrhage (PPH) is defined as cumulative blood loss of 1000 mL or more, or blood loss accompanied by signs and symptoms of hypovolemia, within 24 hours of birth regardless of delivery method. This updated definition from the American College of Obstetricians and Gynecologists (ACOG) replaced the previous threshold of 500 mL for vaginal delivery and 1000 mL for cesarean delivery. PPH is classified as primary (early), occurring within 24 hours of delivery, or secondary (late), occurring between 24 hours and 12 weeks postpartum. Primary PPH accounts for approximately 70-80% of all PPH cases. The pathophysiology of PPH is organized using the 4 Ts mnemonic: Tone, Trauma, Tissue, and Thrombin. Uterine atony (Tone) is the most common cause, accounting for approximately 70-80% of all PPH cases. After placental delivery, the myometrium must contract firmly to compress the spiral arteries at the former placental site. These blood vessels, which carried 500-700 mL/min of blood flow to the placental bed during pregnancy, rely entirely on myometrial contraction (physiological ligatures of Pinard) for hemostasis. When the uterus fails to contract adequately (atony), these...