Uterine Atony and Postpartum Hemorrhage

Introduction

• Description: Uterine atony is the loss of uterine tone after delivery that often manifests as a postpartum hemorrhage. Postpartum hemorrhage is sometimes divided into primary (first 24 hours after delivery) and secondary (up to 12 weeks postpartum), although the causes and management of secondary bleeding are very different and are not covered here.

• Prevalence: Hemorrhage is observed in 5% of deliveries, mostly because of atony (1/20 births; 80% of postpartum hemorrhage); milder degrees are more common. One of the top three causes of maternal mortality (11% of mortality); 1/1000 to as high as 200/1000 in some African countries.

• Predominant Age: Reproductive age.

• Genetics: No genetic pattern.

Etiology and Pathogenesis

• Causes: Loss of the normal uterine contractile forces.

• Risk Factors: Multiparity (grand multiparity), uterine overdistention (multiple birth, polyhydramnios), prolonged labor, prolonged oxytocin stimulation, muscle-relaxant agents (MgSO ₄ , tocolytics), rapid labor, chorioamnionitis, retained placental tissue, obesity, high parity.

Signs and Symptoms

• Bright-red vaginal bleeding

• Loss of uterine tone palpable on abdominal examination

• Tachycardia, hypotension, and vascular collapse possible

• Postpartum hemorrhage is variously defined but is generally blood loss of 1000 mL or more or bleeding greater than expected associated with signs or symptoms of hypovolemia. Older definitions made a distinction between blood loss at vaginal delivery (≥500 mL) and that at cesarean delivery (≥1000 mL). Because morbidity is infrequent with blood loss less than 1000 mL, this lower threshold has been dropped. However, this amount of bleeding following vaginal delivery is still abnormal and should prompt investigation and possible intervention.

Diagnostic Approach