Uterine atony

Failure of the myometrium to contract adequately after delivery, resulting in a soft, enlarged, hypotonic uterus that cannot effectively compress uterine blood vessels. It is the leading cause of primary postpartum hemorrhage.

Causes

• Uterine overdistension

  • Multiple pregnancy (twins)

  • Polyhydramnios

  • Macrosomia

• Prolonged labor

• Extremely rapid labor

• Medication-related causes

  • Magnesium sulfate (MgSO₄)

  • Prolonged or high-dose oxytocin exposure

  • Tocolytic drugs

  • General anesthesia

• Uterine structural causes

  • Uterine fibroids

  • Adenomyosis

  • Uterine anomalies

• Infectious causes

  • Chorioamnionitis

  • Endometritis

• Other causes

  • Placental abnormalities

  • Retained placental tissue

  • Previous uterine atony

  • High parity