What Is It, Risk Factors, Treatment, and More
Author: Nikol Natalia Armata
Editors: Ahaana Singh, Alyssa Haag, Kelsey LaFayette, BAN, RN
Illustrator: Jillian Dunbar
Copyeditor: Joy Mapes
What is uterine atony?
The uterus is anatomically divided into 3 regions; the fundus (uppermost part), the body (main part), and the cervix (lower part). The uterine wall consists of three layers: the perimetrium (outer), myometrium (middle), and endometrium (inner).
After delivery, the uterine muscles of the myometrium usually continue to contract in order to halt bleeding from the spiral arteries, which supply the endometrium with blood. These uterine contractions mechanically reduce the blood flow and consequently increase the likelihood of coagulation, or blood clotting, which can help prevent postpartum hemorrhage (i.e., heavy bleeding after giving birth).With uterine atony, however, the uterine muscles do not contract as needed, putting the individual at risk of postpartum hemorrhage. Uterine atony is considered an obstetric emergency. According to the American College of Obstetricians and Gynecologists, it is the most common cause of postpartum hemorrhage, and globally, it is considered to be one of the main causes of maternal mortality.
What causes uterine atony?
Uterine atony is caused by the inability of the myometrium to contract sufficiently in response to oxytocin, a hormone the body releases before and during childbirth to stimulate uterine contractions.
There are many known risk factors that can increase an individual's chance of developing uterine atony.
An individual is at greater risk if this is their first time giving birth, which is referred to as primiparity, or if they are delivering 5 or more children, known as grand parity. Experiencing a long-lasting labor, marked by a prolonged first stage of labor (i.e., the initial contractions and dilation of the cervix), may also increase the risk of uterine atony in the third stage of labor (i.e., after the infant is delivered). Moreover, excessive exposure to labor-inducing medications, such as synthetic oxytocin, can sometimes desensitize the body and subsequently lead to uterine atony. Additionally, a body mass index (BMI) of 40 or above and history of previous postpartum hemorrhages are also risk factors.
Individuals with an overdistended uterus, or a uterus that is larger than usual, are prone to decreased tone of the uterine muscle tissue, called hypotonia, and therefore are more likely to experience uterine atony. Uterine distention often occurs when a fetus is especially large (i.e., macrosomia), when multiple fetuses are present, or when an excessive amount of amniotic fluid accumulates (i.e., polyhydramnios).
Existing uterine pathologies can constitute an additional risk factor for uterine atony. The presence of fibroids, which are non-cancerous growths made of fibrous and muscle tissue that usually develop in and around the uterus, may impair the contraction of the uterine body. Chorioamnionitis, a bacterial infection that can occur before or during labor, can also be associated with uterine atony.
Less frequently, magnesium sulfate infusion can have a negative impact on uterine contraction. Magnesium sulfate infusion is sometimes given to prevent and treat seizures in pregnant individuals who have high blood pressure, a complication called pre-eclampsia, or pregnant individuals who have eclampsia, which is preeclampsia with the presence of seizures.
Higher risk factors for developing uterine atony include placental disorders, such as placenta accreta or placenta previa, and bleeding diathesis (i.e., increased tendency of the pregnant individual to bleed or bruise).In general, individuals with one of the aforementioned risk factors are classified at medium risk for developing uterine atony, while individuals with 2 or more risk factors are classified at a high risk. For many pregnant individuals with known risk factors, uterine atony can be anticipated in advance of surgery.
What are the signs and symptoms of uterine atony?
The main sign of uterine atony is postpartum hemorrhage, or excessive blood loss after delivery. This can cause a drop in the arterial blood pressure and consequently increase the heart rate. Individuals may also experience pain, especially in the lower back.
How is uterine atony diagnosed?
Uterine atony is usually diagnosed during physical examination immediately upon delivery. After a cesarean delivery, examination to check uterine tone usually involves direct palpation of the uterus. After vaginal delivery, uterine tone can be assessed via indirect bimanual examination, in which the clinician places one hand at the individual’s abdomen while performing a vaginal examination. The examination of an individual with uterine atony will reveal a uterus that seems enlarged and soft, commonly referred to as “boggy.” The uterus will typically contain a significant amount of blood in its cavity and present with bleeding through the vaginal channel. In cases of localized atony, in which the fundus is contracted but the cervix is not, diagnosis might be more difficult.
A bedside obstetric ultrasound can also be performed to confirm the diagnosis. The ultrasound imaging of the uterus may show an echogenic, or bright, stripe inside the uterine cavity, which usually corresponds to the remaining parts of the placenta that were not completely removed during delivery.
How is uterine atony treated?
If uterine atony occurs, healthcare providers should be ready for immediate and efficient intervention.
Initial Medical Treatment
Initial prevention and management of uterine atony requires active management of the third stage of labor. This includes performing uterine massage while gently pulling the end of the umbilical cord in order to detach the entire placenta from the uterine walls. Massaging the uterus can also help promote stronger contractions and push any remaining blood out of the uterus.
In addition, medication may be administered to improve the tone of the uterus and induce uterine contractions. Examples include synthetic oxytocin (Pitocin), which can be administered intravenously or intramuscularly, methylergonovine (Methergine), and prostaglandins, like 15-methyl prostaglandin (Hemabate), misoprostol (Cytotec), and dinoprostone (Prostin E2).
When trying to stop uncontrollable bleeding, obstetricians may initiate tamponade techniques, or the application of pressure to the uterine walls, to limit blood loss. This typically involves packing the uterus and vagina with gauze or inflating the uterine cavity with a Bakri balloon. As these techniques may exert extensive pressure on the bladder, a Foley catheter is typically inserted to empty the bladder.
Surgical Management TechniquesLastly, if conservative management of postpartum hemorrhage fails to resolve the bleeding, surgery may be necessary. The first step is uterine curettage, in which the clinician scrapes the inside of the uterine cavity with a spoon-shaped instrument and removes any retained blood products (e.g., blood clots). Artery ligation, the application of stitches to the main artery that supplies blood to the uterus, is typically the next step. Usually, this is highly effective at controlling bleeding that starts from the uterus; however, if it is not sufficient, a hypogastric artery ligation can also be performed. A hysterectomy, or removal of the uterus, is a final measure reserved for cases of persistent bleeding or dramatic blood loss.
Can uterine atony happen twice?
Yes, uterine atony can happen twice, in two different deliveries. In fact, if an individual has previously experienced uterine atony, they are more likely to experience uterine atony again in a future delivery.
What are the most important facts to know about uterine atony?
Uterine atony refers to the failure of the uterus to contract sufficiently in response to oxytocin during and after childbirth. It is considered an emergency in obstetrics and gynecology, so risk factors should be taken into consideration before labor begins. The main sign of uterine atony is postpartum hemorrhage, with excessive blood loss that can cause hypotension and increased heart rate. During physical examination, the uterus appears soft, enlarged, and filled with blood products. Initial management of uterine atony with uterine massage and appropriate medication is key. However, if uterine atony persists despite initial interventions, tamponade techniques may be initiated, Surgery may be necessary if these conservative methods fail to resolve the bleeding.
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Resources for research and reference
Breathnach, F., & Geary, M. (2009). Uterine atony: Definition, prevention, nonsurgical management, and uterine tamponade. Seminars in Perinatology, 33(2): 82-87. DOI: 10.1053/j.semperi.2008.12.001
Gill, P., Patel, A., Van Hook, J. (2020, July 10). Uterine atony. In StatPearls [Internet]. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK493238/
Kim, M.-L., Hur, Y.-M., Ryu, H., Lee, M. J., Seong, S. J., & Shin, J. S. (2020). Clinical outcomes of prophylactic compression sutures for treatment of uterine atony during the cesarean delivery of twins. BMC Pregnancy and Childbirth, 20(1): 40. DOI: 10.1186/s12884-019-2716-6
Morey, S. (1998). ACOG releases a report on risk factors, causes and management of postpartum hemorrhage. American Family Physician, 58(4): 1002-1004. Retrieved from https://www.aafp.org/afp/1998/0915/p1002.html
Nyfløt, L., Stray-Pedersen, B., Forsén, L., & Vangen, S. (2017). Duration of labor and the risk of severe postpartum hemorrhage: A case-control study. PloS One, 12(4): e0175306. DOI: 10.1371/journal.pone.0175306Society for Endocrinology. (2020). Oxytocin. In You and your hormones. Retrieved March 18, 2021, from https://www.yourhormones.info/hormones/oxytocin/