What Is Uterine Atony?

Uterine atony—also called atony of the uterus—is a complication of pregnancy that occurs after the delivery stage of labor. It is a failure of the uterus to contract following delivery.

It can lead to a very serious—even life-threatening—condition known as postpartum hemorrhage (bleeding) if not treated promptly. Uterine atony is considered the most common cause of postpartum hemorrhage.

This article discusses the causes, symptoms, diagnosis, and treatment of uterine atony.

Causes

There are several factors known to prevent the uterine muscles from contracting after labor, common factors include:

• Overdistension (excessive stretching) or excessive enlargement of the uterus from various causes, including multiple gestation (giving birth to more than one baby at a time) and polyhydramnios (large amount of amniotic fluid)
• Prolonged labor
• Rapid labor
• The use of oxytocin (a hormone used to produce contractions)
• The use of general anesthesia or other drugs during labor

There are several factors linked with an increased risk of uterine atony, including:

• Fetal macrosomia (a fetus that is larger than usual)
• High parity (having many prior births)
• Intra-amniotic infection, or chorioamnionitis (infection of the fetal membranes and amniotic fluid)
• Agents that relax the uterus (such as drugs used for pain management during labor)
• Being more than 35 years old
• Obesity
• A delivery involving forceps or vacuum assistance

It's important to note that uterine atony can occur, even in those without any risk factors present. 

Symptoms

The primary symptom of uterine atony is a relaxed uterus, which is one that shows no signs of tightness or tension after birth. When palpated (manually felt) after delivery by a healthcare provider, the uterus may feel boggy (spongy) or enlarged.

The symptoms of postpartum hemorrhage—caused by uterine atony—include:

• Uncontrollable bleeding
• Low blood pressure
• An increase in heart rate (pulse)
• Back pain
• Other pain

Complications (Hemorrhage)

Complications of uterine atony may include:

• Orthostatic/postural hypotension: dizziness from low blood pressure that commonly occurs when a person gets up after sitting or lying down
• Anemia: low red blood cell count
• Hypovolemic shock: a serious, potentially life-threatening complication of uterine atony, involving low blood volume from the loss of blood or other fluids

Hemorrhagic shock is hypovolemic shock from blood loss. Symptoms of hypovolemic shock and hemorrhagic shock include:

• Profuse bleeding
• Pale, cool skin
• Diaphoresis (profuse sweating)
• Tachycardia (fast heart rate/rapid pulse)
• Rapid breathing
• Lethargy (extreme fatigue, confusion, and possibly unconsciousness)

Diagnosis

When there are signs of excessive bleeding, and the uterus feels boggy, soft, and relaxed, after a person gives birth, a diagnosis of uterine atony is often made.

Blood loss could be calculated by assessing the number of saturated sanitary pads or by weighing the pads or sponges used to absorb the blood.

Other sources of bleeding (such as a tear in the cervix or vagina) will be ruled out.

Signs and symptoms will be monitored closely to screen for complications—such as anemia or hypovolemic shock. These may include close observation of blood pressure, pulse, red blood cell count, and more.

Treatment

Uterine atony can usually be managed by manual massage of the uterus, along with medications to promote uterine contractions (called uterotonic drugs).

These drugs help enhance contractions of the uterus and control bleeding, they include:

• Oxytocin
• Methergine
• Prostaglandins (such as Hemabate)
• Ergot alkaloids
• Misoprostol

For cases of uterine atony, with complications, other treatment may be necessary to replace fluids and blood loss such as:

• Intravenous (IV) fluids
• Blood transfusions
• Blood products

Treatment for very severe uterine atony with complications may include:

• Surgery: To tie off blood vessels
• Uterine artery embolization: Blocking the flow of blood to the uterus
• Hysterectomy: Surgical removal of the uterus when all other measures fail

Frequently Asked Questions

How does uterine atony cause postpartum hemorrhage?

Postpartum hemorrhage is strongly linked with uterine atony. This is because uterine contractions are instrumental in assisting with the blood clotting process and helping the uterus to stop bleeding after delivery (particularly after the placenta is delivered).

How common is uterine atony?

Somewhat common, as uterine atony occurs in approximately one in every 40 births (2.5%) in the United States. However, the condition is very serious because it's responsible for at least 80% of postpartum hemorrhage cases.

How is uterine atony treated?

Uterine atony is treated differently depending on the severity of the condition and any complications present. Primarily, treatment aims to promote uterine contractions and stop bleeding.

Uterine massage after delivery as well as the administering of oxytocin is a common preventive practice today.