What are the causes of urinary retention in pregnancy?

Causes of Urinary Retention in Pregnancy

Urinary retention in pregnancy is most commonly caused by a retroverted, impacted gravid uterus trapped in the pelvis, typically occurring in the late first or early second trimester (10-18 weeks gestation), with additional risk factors including uterine fibroids, pelvic adhesions from prior surgery or infection, and rarely urethral obstruction. 1, 2, 3

Primary Mechanical Causes

Impacted Retroverted Uterus

• The enlarging gravid uterus becomes trapped within the pelvic ring and fails to ascend into the abdominal cavity, causing compression of the bladder neck or urethra 3, 4
• This is the most common etiology of antenatal urinary retention 3
• Typically manifests between 10-18 weeks gestation when the uterus reaches critical size but remains confined 2, 3

Uterine Fibroids

• Large posterior uterine fibroids (≥6 cm) can contribute to uterine impaction and bladder compression 5
• Fibroids prevent normal uterine ascent from the pelvis as pregnancy progresses 4

Pelvic Adhesions

• Prior pelvic inflammatory disease creates scar tissue that traps the uterine fundus and prevents normal anatomical positioning 3, 4
• Previous abdominal or pelvic surgery leads to severe adhesions causing persistent uterine retroversion 3

Less Common Causes

Urethral Obstruction

• Direct urethral obstruction can occur, though this is rare 3
• May initially present as urinary tract infection due to incomplete bladder emptying 3

Epidemiology and Clinical Context

• Antenatal urinary retention occurs in approximately 1 in 1,000 pregnancies (0.92/1000) 1
• Most cases occur in late first trimester and early second trimester 1
• Risk factors can be identified in only a minority of cases; most women have uncomplicated pregnancies before developing acute retention 1

Important Clinical Pitfalls

Delayed Recognition

• Clinicians may focus on gastrointestinal symptoms and miss the inability to void, leading to severe complications including spontaneous abortion 3
• Covert retention (incomplete emptying without obvious voiding difficulty) may go unrecognized, as most women deny specific bladder symptoms including difficulty voiding or incomplete emptying 1

Serious Complications if Untreated

• Bladder rupture is a life-threatening but entirely preventable complication 4
• Severe electrolyte imbalances including syndrome of inappropriate antidiuretic hormone secretion (SIADH) with severe hyponatremia can occur, requiring ICU admission 5
• Miscarriage and uterine rupture are potential consequences of delayed diagnosis 2, 4

Risk Factor Summary

The following increase likelihood of antenatal urinary retention:

• Uterine retroversion 3, 4
• History of pelvic inflammatory disease 3, 4
• Large uterine fibroids, particularly posterior location 5, 4
• Previous pelvic or abdominal surgery 3
• Gestational age 10-18 weeks (critical period for uterine impaction) 2, 3