Uterine atony
Synonyms and keywords:

# Overview
Physiologically, contraction of the myometrium occurs in response to oxytocin, therefore, mediates the uterine hemostasis by mechanically compressing the blood vessels supplying the placenta. The uterine atony is caused by inadequate contraction of the myometrium following the delivery. Uterine atony must be differentiated from other diseases that cause postpartum hemorrhage, such as retained placental tissue, obstetric lacerations,  placenta accreta spectrum (placenta accreta, increta, and percreta), uterine inversion, maternal coagulation defects, and disseminated intravascular coagulation (DIC). Uterine atony is responsible for up to 80% of cases of postpartum hemorrhage, and approximately 25% of maternal deaths are due to postpartum hemorrhage, which is the leading cause of maternal deaths. The presence of a large, soft and boggy uterus on physical examination is highly suggestive of uterine atony. The mainstay of treatment for uterine atony is bimanual uterine massage with the administration of oxytocin (IV or IM) simultaneously. If oxytocin fails, second-line pharmacologic agents (methylergonovine or carboprost) should be considered. If medical therapy fails, surgical procedures such as uterine compression sutures (brace sutures) should be considered.

# Historical Perspective
In 1953, Du Vigneaud et al. were the first to discover the aminoacid sequence of oxytocin and its biochemical synthesis. Following his discoveries about polypeptide hormones, The Nobel Prize for chemistry was awarded to Vincent du Vigneaud in 1955.

# Classification
There is no established system for the classification of uterine atony.

# Pathophysiology
It is thought that the uterine atony is caused by inadequate contraction of the myometrium following the delivery. Physiologically, contraction of the myometrium occurs in response to oxytocin, therefore, mediates the uterine hemostasis by mechanically compressing the blood vessels supplying the placenta.

# Causes and Risk Factors
Common risk factors in the development of uterine atony include:
- Uterine overdistention
Polyhydramnios
Multiple pregnancy
Macrosomia
- Polyhydramnios
- Multiple pregnancy
- Macrosomia
- Intrinsic factors
Advanced maternal age
Obesity
Maternal race/ethnicity (Hispanic and non-Hispanic white)
Previous postpartum hemorrhage
Anemia
Preeclampsia
Fibroids
- Advanced maternal age
- Obesity
- Maternal race/ethnicity (Hispanic and non-Hispanic white)
- Previous postpartum hemorrhage
- Anemia
- Preeclampsia
- Fibroids
- Delivery-related factors
Prolonged labor
Precipitate labor
Prolonged use of oxytocin
Induction of labor
Manual removal of placenta
- Prolonged labor
- Precipitate labor
- Prolonged use of oxytocin
- Induction of labor
- Manual removal of placenta
- Chorioamnionitis
- Administration of magnesium sulfate
- Administration of inhaled anesthetic agents

# Differentiating Uterine Atony from other Diseases
Uterine atony must be differentiated from other diseases that cause postpartum hemorrhage, such as retained placental tissue, obstetric lacerations,  placenta accreta spectrum (placenta accreta, increta, and percreta), uterine inversion, maternal coagulation defects, and disseminated intravascular coagulation (DIC)
- Detection of the uterine atony might be challenging in the presence of uterine inversion which causes the absence of typical findings of uterine atony such as soft and boggy uterus. The specific finding of uterine inversion is a visible protruding mass through the vagina.

# Epidemiology and Demographics
Uterine atony is responsible for up to 80% of cases of postpartum hemorrhage, and approximately 25% of maternal deaths are due to postpartum hemorrhage, which is the leading cause of maternal deaths.

# Screening
There is insufficient evidence to recommend routine screening for uterine atony. However, identifying the risk factors might provide a better prediction of women at risk for uterine atony, therefore, planning and preparation might be provided more sufficiently.

# Natural History, Complications, and Prognosis
- Previous history of postpartum hemorrhage increases the risk of recurrence by up to 15% in the next pregnancy.
- Common complications of uterine atony include:
Postpartum anemia
Hypovolemic shock
Disseminated intravascular coagulation (DIC)
Transfusion-associated morbidities (transfusion-related acute lung injury (TRALI), transfusion-associated volume overload)
Acute respiratory distress syndrome (ARDS)
Uterine necrosis
Sheehan syndrome
- Postpartum anemia
- Hypovolemic shock
- Disseminated intravascular coagulation (DIC)
- Transfusion-associated morbidities (transfusion-related acute lung injury (TRALI), transfusion-associated volume overload)
- Acute respiratory distress syndrome (ARDS)
- Uterine necrosis
- Sheehan syndrome

# Diagnosis

## Diagnostic Study of Choice
For the diagnostic definition of postpartum hemorrhage, click here.

## History and Symptoms
- A detailed prenatal history is important for the detection of risk factors in the development of uterine atony.
- The hallmark of postpartum hemorrhage is hypovolemia. For more symptoms of postpartum hemorrhage, click here.

## Physical Examination
Abdominal examination by palpation is one of the main methods of physical examination in the diagnosis of uterine atony. Palpation of the uterus might be either direct (following the cesarean delivery) or indirect (bimanual examination after the vaginal delivery).
- The presence of a large, soft and boggy uterus on physical examination is highly suggestive of uterine atony.
- In case of focal localized atony of the uterine lower segments with normal contraction of uterine fundus, it might be challenging to detect the uterine atony with abdominal examination. Thus, manual exploration of the uterine cavity or ultrasound imaging might be useful in suspected cases.

## Laboratory Findings
Laboratory findings consistent with the diagnosis of uterine atony include a decreased concentration of hemoglobin and hematocrit.
- Severe anemia (Hb  7 g/dl) might decrease the ability of contraction of the myometrium. Therefore, low maternal hemoglobin levels at the beginning of the delivery might predict the possibility and the severity of the uterine atony.

## Electrocardiogram
There are no ECG findings associated with uterine atony.

## X-ray
There are no x-ray findings associated with uterine atony.

## Ultrasound
Ultrasound may be helpful in the diagnosis of uterine atony. Findings on ultrasound suggestive of uterine atony include echogenic endometrial stripe and intrauterine blood clots with no intrinsic vascularity.
- On the other hand, findings on ultrasound suggestive of retained products of conception, which is another cause of postpartum hemorrhage, include intrauterine mass with intrinsic vascularity.

## CT scan
Dynamic CT (dCT) scan may be helpful in the detection of intractable uterine atony. Findings on dCT scan suggestive of intractable uterine atony include arterial contrast extravasation and significant difference of size and shape between the upper and lower uterine cavity.
- The eventual requirement of embolization might be predicted by the presence of arterial contrast extravasation on dynamic CT scan.

## MRI
There are no MRI findings associated with uterine atony.

## Other Imaging Findings
There are no other imaging findings associated with uterine atony.

## Other Diagnostic Studies
There are no other diagnostic studies associated with uterine atony.

# Treatment

## Medical Therapy
The mainstay of treatment for uterine atony is bimanual uterine massage with the administration of oxytocin (IV or IM) simultaneously.
- It is thought that the stimulation of uterine contractions can be mediated by bimanual uterine massage by the secretion of endogenous prostaglandins.
If oxytocin fails, second-line pharmacologic agents (methylergonovine or carboprost) should be considered.
- Methylergonovine is generally preferred as a second-line pharmacologic treatment. However, it should be avoided in patients with hypertension and cardiovascular diseases.
- Carboprost should be avoided in patients with asthma, cardiovascular diseases, hepatic diseases, and renal diseases.
If pharmacotherapy fails, uterine compression sutures or placement of a uterine balloon tamponade (success rate >85%) such as Bakri balloon tamponade may be considered.

## Surgery
Surgery is not the first-line treatment option for patients with uterine atony. Surgery is usually reserved for patients with bleeding resistant to the medical therapy.
- Uterine compression sutures (brace sutures) such as the B-Lynch method is recommended in patients with uterine atony resistant to the medical therapy (bimanual uterine massage, administration of uterotonic agents, etc.).
Possible complications of uterine compression sutures include intrauterine synechiae and uterine necrosis.
- Possible complications of uterine compression sutures include intrauterine synechiae and uterine necrosis.
- If uterine compression sutures or balloon tamponades fail, bilateral uterine artery ligation should be considered as a next step treatment approach.
- If the bleeding is still poorly controlled, the next step should be the ligation of the bilateral utero-ovarian artery.
- If the bleeding continues, ligation of the internal iliac artery should be considered.
- If all the abovementioned procedures are not successful for the bleeding control (might be considered at an earlier step for patients without fertility desires), hysterectomy (total or supracervical) should be considered as a life-saving measure.
Possible complications of hysterectomy include infections of the female genitourinary system, venous thromboembolism, ileus, postoperative hemorrhage, Clostridium difficile infection, bowel injuries, urinary tract injuries, vaginal cuff dehiscence, urinary incontinence, sexual dysfunction, hormonal changes, anorectal injuries, and nerve injuries with neuropathies.
- Possible complications of hysterectomy include infections of the female genitourinary system, venous thromboembolism, ileus, postoperative hemorrhage, Clostridium difficile infection, bowel injuries, urinary tract injuries, vaginal cuff dehiscence, urinary incontinence, sexual dysfunction, hormonal changes, anorectal injuries, and nerve injuries with neuropathies.

## Prevention
For the prevention of postpartum hemorrhage, click here.