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Primary postpartum hemorrhage most commonly results from uterine atony, in which the myometrium fails to contract effectively, leaving uterine spiral arteries patent. A soft, enlarged (“boggy”) uterus with heavy bleeding shortly after delivery is diagnostic. First-line treatment is immediate bimanual uterine massage to stimulate contraction coupled with uterotonic therapy—oxytocin is the agent of choice due to rapid onset and favorable safety profile. If bleeding persists, second-line uterotonics include methylergonovine (contraindicated in hypertension or preeclampsia due to vasoconstriction) and carboprost (contraindicated in asthma due to bronchospasm risk). Tranexamic acid can be used adjunctively to stabilize clots but is not a substitute for uterine contraction. Broad-spectrum antibiotics (choice A) treat postpartum endometritis, which presents with uterine tenderness and fever, not acute atony. Additional measures for refractory hemorrhage include intrauterine balloon tamponade (Bakri balloon), uterine artery embolization, or surgical interventions (B-Lynch suture, hysterectomy) depending on response and stability. Rapid assessment with uterine massage and oxytocin is life-saving and reduces transfusion needs.