PATHOPHYSIOLOGY OF UTERINE MUSCLE CONTRACTION AND ONSET OF LABOR: FROM MYOMETRIAL ACTIVATION TO PHYSIOLOGICAL BLOOD LOSS

Labor begins when the uterus shifts from relative quiescence to coordinated contractility. Objective:This review analyzes the pathophysiology of uterine muscle contraction, biological readiness forlabor and the boundary between physiological and dangerous blood loss. Methods: Internationalguidelines and reviews on intrapartum care, postpartum hemorrhage and uterotonic use wereexamined. Results: Myometrial activation depends on gap-junction formation, oxytocin sensitivity,prostaglandin activity, cervical remodeling and inflammatory signaling. Discussion: Understandingcontraction physiology improves interpretation of labor progress and hemorrhage prevention.Conclusion: The uterus is both the engine of birth and the main organ preventing postpartumbleeding; therefore, contraction biology is central to safe obstetrics