Uterine atony is a serious complication of childbirth that can occur following either a vaginal delivery or a cesarean section. It is the single most frequent cause of postpartum hemorrhage, defined as excessive bleeding after birth. Because it can lead to rapid and dangerous blood loss, uterine atony is considered an obstetric emergency. Healthcare professionals are trained to recognize the warning signs and manage this situation swiftly.
Defining Uterine Atony
Uterine atony refers to a lack of muscle tone in the uterus, meaning the myometrium fails to contract adequately after delivery. Normally, the uterus is a powerful muscle that performs sustained contractions during labor. After the placenta separates from the uterine wall, the blood vessels that supplied it are left open and bleeding.
The body’s natural mechanism to stop this bleeding relies on the uterine muscle fibers physically squeezing and compressing the blood vessels. This contraction acts like a “living ligature,” clamping down on the vessels to achieve hemostasis. A uterus that has contracted properly should feel firm and hard.
When uterine atony occurs, this necessary muscular compression is insufficient or absent. The uterine muscle remains soft, weak, and relaxed, often described as “boggy,” leaving the blood vessels wide open. This failure allows blood to flow freely from the placental site, resulting in significant hemorrhage. Uterine atony is responsible for up to 80% of all cases of postpartum bleeding.
Causes and Risk Factors
The failure of the uterus to contract is often related to conditions that cause the muscle to become overstretched, fatigued, or inhibited. One major risk factor is overdistention of the uterus. This occurs with multiple gestation (twins or triplets), an excessive amount of amniotic fluid (polyhydramnios), or a very large baby (fetal macrosomia).
The duration and nature of labor also play a role, as both prolonged and very rapid labor can lead to uterine muscle fatigue. Certain medical interventions and conditions increase the risk, including the use of magnesium sulfate to treat preeclampsia, or an infection of the membranes (chorioamnionitis). A history of uterine atony in a previous delivery also increases the risk of recurrence.
Recognizable Signs and Symptoms
The most immediate sign of uterine atony is rapid, heavy, and prolonged vaginal bleeding following delivery. While some blood loss is expected after childbirth, the excessive nature of the bleeding is the primary indicator of a problem. This flow quickly leads to secondary signs indicating the body is struggling to cope with the blood loss.
Healthcare providers confirm the diagnosis through a physical examination of the uterus. When palpated externally, an atonic uterus feels soft, flabby, or “boggy,” rather than firm and contracted. Other observable symptoms relate to circulatory distress from blood loss, including a rapid heart rate, low blood pressure, pale appearance, and dizziness or fainting.
Medical Management and Treatment
The management of uterine atony follows a rapid, stepwise approach, beginning with immediate physical intervention. The first action is typically a vigorous manual uterine massage, performed by a provider placing one hand on the abdomen and the other performing a vaginal examination to compress the uterus. This manual stimulation encourages the myometrium to begin contracting.
Simultaneously, pharmacological agents known as uterotonics are administered to stimulate strong uterine contractions. Oxytocin is the first-line drug, given intravenously or intramuscularly to encourage rhythmic muscular activity. If the bleeding continues, other powerful uterotonics are used, such as methylergonovine (an ergot alkaloid) or prostaglandin medications like misoprostol or carboprost, which each have specific contraindications.
If these primary methods fail to stop the hemorrhage, the medical team progresses to more advanced interventions. These include uterine tamponade techniques, such as placing an intrauterine balloon or packing the uterus with gauze to apply direct pressure to the bleeding vessels. Surgical procedures are reserved for refractory cases and may involve placing compression sutures, such as B-Lynch sutures, across the uterus to mechanically compress the muscle. As a measure of last resort, a hysterectomy (removal of the uterus) may be required to save the patient’s life.