Uterine Atony

What uterine atony is

During pregnancy, the uterus receives about 500 to 800 ml of blood every minute. After the placenta separates, the wound it leaves would bleed heavily if the muscle did not act. The uterine muscle fibers are arranged in a crisscross pattern, and when they contract, they squeeze the blood vessels shut. Doctors call these "living ligatures".

In uterine atony, the muscle is too tired, stretched, inflamed or relaxed to contract properly. The uterus feels soft and large, often above the navel, instead of firm like a grapefruit around or below it. Blood pours from the placental bed and can reach dangerous volumes within minutes.

Uterine atony is one of the "4 Ts" of postpartum hemorrhage:

Causes and risk factors

Overstretched uterus

• Twins or more
• A large baby (over about 4 kg or 8.8 lb)
• Excess amniotic fluid (polyhydramnios)

A tired uterus

• Long labor, or a very fast labor
• High doses or long use of oxytocin to induce or speed up labor
• Many previous births

Things that relax the uterus or stop it contracting

• Infection of the membranes during labor (chorioamnionitis)
• Some medicines: magnesium sulfate (used in preeclampsia), general anesthesia with inhaled agents, and drugs that stop contractions
• Uterine fibroids that disrupt the muscle
• Retained placenta or clots preventing full contraction
• A full bladder pushing on the uterus

Other

• Previous postpartum hemorrhage
• Cesarean birth
• Placental abruption and placenta previa
• Obesity and maternal age over 35

Many cases happen in people with no risk factors, so every birth is managed as if hemorrhage could happen.

Signs and symptoms

• Heavy bleeding from the vagina immediately after the placenta is delivered or in the next hours
• Large clots
• A soft, enlarged uterus felt through the belly, which firms up briefly with massage then relaxes again
• Signs of significant blood loss: fast heartbeat, lightheadedness, low blood pressure, pale clammy skin, restlessness, and reduced urine, leading to hypovolemic shock

Young, healthy people can lose a large amount of blood before blood pressure falls, so rising heart rate is an important early sign. Blood loss is often underestimated by eye, so many hospitals now weigh or measure blood.

Diagnosis

Uterine atony is diagnosed at the bedside: heavy bleeding with a soft, poorly contracted uterus. The team rapidly checks for the other causes: tears in the birth canal, retained placental tissue (by inspecting the placenta and with ultrasound), and clotting problems with blood tests. Vital signs, blood count, clotting tests and cross-matching for transfusion are done at the same time.

Treatment

Treatment is stepwise and fast, with the obstetric team, anesthesiologists and blood bank working together.

1. Uterine massage: firm, rhythmic rubbing of the top of the uterus through the belly, or compression between a hand in the vagina and a hand on the belly (bimanual compression).
2. Emptying the bladder with a catheter.
3. Uterotonic medicines that make the uterus contract: - Oxytocin by IV drip or injection (first-line) - Methylergonovine (avoided with high blood pressure or preeclampsia) - Carboprost (avoided in asthma) - Misoprostol
4. Tranexamic acid within 3 hours of birth, which reduces deaths from bleeding.
5. Fluids and blood transfusion, including plasma, platelets and fibrinogen if needed.
6. Intrauterine balloon tamponade: a balloon inflated inside the uterus to press on the bleeding surface, or a vacuum-induced device that helps the uterus contract.
7. Interventional radiology: blocking the uterine arteries with tiny particles (embolization) in stable patients.
8. Surgery: compression sutures that wrap the uterus (such as the B-Lynch suture), tying off the uterine arteries, and as a last resort, hysterectomy.

Complications

• Severe anemia and tiredness for weeks
• Need for blood transfusion
• Disseminated intravascular coagulation, where clotting factors are used up
• Kidney injury, breathing problems and admission to intensive care
• Pituitary damage from severe blood loss (Sheehan syndrome), causing failure to breastfeed and hormone problems
• Loss of future fertility if hysterectomy is needed
• Emotional trauma and postnatal depression or PTSD

Prevention

• Active management of the third stage of labor: giving oxytocin to every birthing person immediately after the baby is born, which reduces postpartum hemorrhage substantially
• Planning for people at high risk: delivering in a hospital with blood bank access, IV access during labor, and blood cross-matched
• Treating anemia during pregnancy so there is more reserve if bleeding occurs
• Emptying the bladder and checking that the uterus is firm after delivery

Recovery and future pregnancies

Most people recover fully, though tiredness from blood loss can last weeks. Iron supplements and sometimes iron infusions rebuild blood counts. Having had uterine atony raises the risk in a future pregnancy, so tell your prenatal provider. They will plan the birth with this in mind.

Frequently asked questions

What is uterine atony?

Uterine atony is when the uterus does not contract firmly enough after childbirth. Without strong contractions, the blood vessels where the placenta was attached keep bleeding. It is the most common cause of postpartum hemorrhage and is treated with massage, medicines and sometimes procedures.

What causes uterine atony?

Common causes include an overstretched uterus from twins, a large baby or excess fluid, a long or very fast labor, prolonged oxytocin use, infection during labor, fibroids, some anesthetic drugs and magnesium sulfate. It can also happen without any risk factors, which is why preventive oxytocin is routine.

How is uterine atony treated?

The team massages the uterus and gives medicines such as oxytocin, methylergonovine, carboprost or misoprostol to make it contract, plus tranexamic acid to reduce bleeding. If bleeding continues, a balloon inside the uterus, artery embolization or surgery such as compression sutures can control it. Hysterectomy is a last resort.

Can uterine atony happen days after birth?

Most atony occurs within the first 24 hours. Heavy bleeding from 24 hours to 12 weeks after birth is called secondary postpartum hemorrhage and is more often due to retained tissue or infection, which can also keep the uterus from contracting. Any heavy bleeding after birth needs urgent care.

Will I have uterine atony again in my next pregnancy?

Your risk is higher than average but most people do not have it again. Your care team will plan accordingly, for example with delivery in a hospital, IV access, blood available, and medicines ready immediately after the birth. Treating anemia during pregnancy also helps.