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

Abstract

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