Uterine Atony

What is Uterine atony?

Uterine atony occurs when the myometrium, the muscular middle layer of the uterine wall, fails to contract effectively following the delivery of the placenta. It is the most common cause of postpartum hemorrhage because inadequate uterine contraction prevents compression of the placental bed vessels, allowing ongoing bleeding.

Uterine atony can rapidly cause hemodynamic instability, requiring rapid resuscitation. It is one of the leading causes of maternal mortality worldwide, especially where rapid obstetric care and blood products are limited. Promptly identifying a soft, poorly contracted fundus (the top portion of the uterus) within minutes of delivery signals a critical emergency.

What causes Uterine atony?

Several physiological factors contribute to the causes of uterine atony by reducing effective myometrial contraction. Overdistension of the uterus stretches muscle fibers beyond their functional limit. This occurs most often in cases of multifetal gestation (carrying more than one fetus) or polyhydramnios (excessive amniotic fluid).

Additionally, prolonged labor and chorioamnionitis (infection of the fetal membranes) can lead to muscle exhaustion and inflammatory damage. Important risk factors of uterine atony include grand multiparity (having given birth multiple times), therapeutic magnesium sulfate use, and a history of previous hemorrhage. Volatile anesthetic agents can worsen uterine relaxation, and retained placental tissue should prompt evaluation for a concurrent tissue cause of postpartum hemorrhage.

What signs and symptoms are associated with Uterine atony?

The most prominent sign is a soft, boggy fundus, which refers to a uterus that feels spongy rather than firm upon palpation. This lack of tone results in immediate, heavy vaginal bleeding and the rapid development of maternal tachycardia (fast heart rate). As blood loss progresses, low blood pressure and other signs of hypovolemia may develop.

Clinicians must differentiate between subinvolution vs uterine atony to determine the appropriate management. Uterine atony occurs immediately postpartum and involves a boggy fundus with brisk bleeding. In contrast, subinvolution arises days or weeks later and features persistent lochia (postpartum discharge) as the uterus fails to return to its normal size.

How is Uterine atony diagnosed?

Diagnosis is primarily through physical assessment immediately following the third stage of labor. A poorly contracted fundus is identified through bimanual palpation while observing for excessive blood loss despite active management. Frequent measurement of blood loss and fundal height helps the team track the severity of the crisis.

Laboratory evaluations, such as a complete blood count and coagulation studies, assess the individual’s physiologic stability. If the uterus remains boggy after initial interventions, a bedside ultrasound can help evaluate for retained placental fragments. The immediate goal is to identify the cause of bleeding and escalate treatment without delay.

How is Uterine atony treated?

The foundation of uterine atony treatment begins with immediate fundal massage and the evacuation of trapped blood clots. Clinicians must also ensure the bladder is empty, as a full bladder can displace the uterus and prevent effective contraction. Pharmacological management typically starts with an intravenous infusion of oxytocin to stimulate myometrial activity and maintain uterine tone.

Guidelines recommend administering tranexamic acid for uterine atony as an adjunct for postpartum hemorrhage as early as possible and within 3 hours of diagnosis. If initial uterotonics fail, providers may add methylergonovine, carboprost, or misoprostol while respecting individual contraindications. Refractory cases may require advanced interventions such as uterine balloon tamponade, compressive sutures, or an emergency hysterectomy to control the bleeding.

What are the most important facts to know about Uterine atony?

• Uterine atony involves the failure of the myometrium to contract after delivery, which is the leading cause of postpartum hemorrhage.
• Common risk factors of uterine atony include uterine overdistension, prolonged labor, maternal infections, and the use of magnesium therapy.
• Early recognition relies on finding a boggy, enlarged uterus with excessive bleeding immediately after delivery, and distinguishing subinvolution vs uterine atony based on the timing of the bleeding.
• Diagnosis is clinical and requires uterine palpation, quantitative blood loss measurement, and potentially bedside ultrasound.
• Rapid uterine atony treatment utilizes fundal massage, uterotonic medications, and the early use of tranexamic acid.
• Refractory cases require escalation to advanced hemorrhage-control measures such as uterine tamponade, compression sutures, embolization, or hysterectomy.