What is an incarcerated uterus?

What is an Incarcerated Uterus?

An incarcerated uterus is a rare obstetric complication in which the gravid (pregnant) uterus becomes trapped or wedged in the posterior pelvis, typically between the sacral promontory and pubic symphysis, preventing its normal ascent out of the pelvis as pregnancy progresses beyond 12-16 weeks gestation. 1, 2, 3

Definition and Anatomical Features

• An incarcerated gravid uterus occurs when a retroverted or retroflexed uterus fails to spontaneously revert to its normal anteverted position and becomes mechanically trapped in the pelvis after 16 weeks of gestation 4
• The uterine fundus becomes wedged behind the sacral promontory, with the cervix displaced anteriorly and superiorly toward the pubic symphysis 2, 5, 3
• This anatomical distortion prevents the normal physiologic ascent of the enlarging uterus into the abdominal cavity 2

Clinical Presentation

The clinical symptoms are highly variable and non-specific, which frequently leads to misdiagnosis 1:

• Urinary retention is the most common presenting symptom, occurring as the trapped uterus compresses the urethra 1, 5, 3
• Lower abdominal or pelvic pain 1, 4
• Low back pain 3
• Nausea and vomiting 3
• Symptoms typically manifest in the early to mid-second trimester (14-20 weeks gestation) when the enlarging uterus should normally be ascending out of the pelvis 1, 4

Risk Factors and Etiology

• Pelvic adhesions from prior surgery, endometriosis, or pelvic inflammatory disease are the most common predisposing factors 1, 5
• Uterine fibroids, particularly posterior wall fibroids 1
• Adenomyosis 4
• Congenital uterine anomalies 1
• Importantly, incarceration can occur even in patients with no prior surgical history, suggesting that adhesive disease may develop from other causes 5
• Among 14 cases reviewed, 13 patients (93%) had some gynecological complication or relevant history 4

Incidence and Natural History

• The incidence is approximately 1 in 3,000 to 1 in 10,000 pregnancies, though exact rates vary 1, 4
• Approximately 1 in 2,300 pregnancies remain incarcerated at term or near-term 4
• Spontaneous resolution occurs in approximately 78.5% of cases after 16 weeks gestation, with the uterus naturally ascending as it enlarges 4
• Resolution can occur as late as the early third trimester in some cases 4
• Three patterns of resolution exist: before late second trimester (6/14 cases), late second to early third trimester (5/14 cases), or persistent incarceration at term (3/14 cases) 4

Diagnostic Approach

Imaging Modalities

• Abdominal and transvaginal ultrasound can establish the diagnosis by directly imaging the disturbed uterine and pelvic anatomy 1
• Ultrasound demonstrates the uterine fundus positioned posteriorly and inferiorly, trapped behind the sacral promontory 2, 5
• MRI provides definitive diagnosis with characteristic imaging features and is particularly useful when ultrasound findings are equivocal 2, 3
• MRI clearly delineates the relationship between the incarcerated uterus, sacral promontory, and surrounding pelvic structures 2

Key Diagnostic Pitfalls

• Misdiagnosis as placenta previa is a critical error that can occur because the anteriorly displaced cervix may be mistaken for the lower uterine segment, leading to incorrect surgical planning and potential catastrophic hemorrhage during cesarean delivery 4
• The non-specific clinical presentation often leads to delayed diagnosis 1
• Physical examination alone is insufficient; imaging confirmation is essential 1, 2

Management Options

Conservative Management

• Expectant management with careful monitoring is appropriate for asymptomatic or minimally symptomatic cases, given the high rate of spontaneous resolution (78.5%) 4
• Foley catheter placement for urinary retention provides symptomatic relief while awaiting spontaneous resolution 1
• Serial ultrasound monitoring to document uterine position and fetal well-being 4

Manual Reduction

• Manual repositioning under anesthesia (spinal or general) can be attempted when conservative measures fail 1, 5
• The knee-chest position may facilitate manual reduction 1
• Success rates vary, and multiple attempts may be unsuccessful 5

Surgical Intervention

• Laparoscopic adhesiolysis is indicated when manual reduction fails and symptoms persist, particularly when dense posterior adhesions are identified 5
• Diagnostic laparoscopy can identify and lyse adhesions between the uterus and surrounding structures (sigmoid mesentery, pelvic sidewall) 5
• Intraoperative transabdominal ultrasound should be used to confirm fetal viability and document successful uterine repositioning 5

Critical Management Caveat

• Even technically successful surgical reduction does not guarantee favorable pregnancy outcomes 5
• One case demonstrated that despite successful laparoscopic adhesiolysis and uterine repositioning, the patient subsequently developed chorion-amnion separation, preterm premature rupture of membranes, and intrauterine fetal demise at 22 weeks, with placental pathology showing severe chorioamnionitis and uteroplacental underperfusion 5
• Close antenatal surveillance is mandatory following any intervention, as anatomical correction does not preclude infectious or vascular complications 5

Complications and Outcomes

Maternal Complications

• Persistent urinary retention requiring prolonged catheterization 1
• Acute kidney injury from obstructive uropathy 1
• Uterine rupture (rare but catastrophic) 1
• Surgical complications during cesarean delivery if incarceration is unrecognized 4
• Massive hemorrhage from cervical injury during misdiagnosed cesarean delivery 4

Fetal Complications

• Intrauterine growth restriction from uteroplacental insufficiency 5
• Preterm delivery 5
• Intrauterine fetal demise 5
• Increased perinatal morbidity and mortality if condition remains undiagnosed 2

Clinical Algorithm

1. Suspect incarcerated uterus in any pregnant patient presenting with urinary retention, pelvic pain, or inability to palpate fundus at expected gestational age in second trimester 1, 3

2. Obtain imaging immediately: Start with transabdominal and transvaginal ultrasound; proceed to MRI if diagnosis uncertain 1, 2

3. Confirm diagnosis by identifying uterine fundus wedged behind sacral promontory with anterior cervical displacement 2, 5

4. Rule out placenta previa carefully to avoid misdiagnosis 4

5. For asymptomatic or mild symptoms: Expectant management with Foley catheter if needed and serial ultrasound monitoring 4

6. For persistent symptoms after 18-20 weeks: Attempt manual reduction under anesthesia 1, 5

7. If manual reduction fails: Consider laparoscopic adhesiolysis with intraoperative ultrasound guidance 5

8. Following any intervention: Intensive antenatal surveillance with serial ultrasounds, given risk of chorioamnionitis, placental insufficiency, and preterm complications 5