A 37-year-old woman, gravida 2 para 1, at 28 weeks gestation comes to the office due to leakage of urine. The patient has had intermittent leakage with cough but no dysuria or hematuria. She reports normal fetal movement and has had an uncomplicated pregnancy. Four years ago, the patient had a spontaneous vaginal delivery of a 3500 g (7 lb 11 oz) neonate. The patient has no chronic medical conditions or prior surgeries. Vital signs are normal. Prepregnancy BMI was 32 kg/m2. She has gained 15.8 kg (34.8 lb) during this pregnancy. The abdomen is gravid, and there is no suprapubic tenderness. Urinalysis is negative for blood, leukocyte esterase, and nitrite. Which of the following is the most likely mechanism for this patient's urinary incontinence?
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This patient with leakage of urine with coughing has stress urinary incontinence (SUI), a common condition during pregnancy. Risk factors include increasing parity, age, BMI, and maternal weight gain, as in this patient.
Several physiologic changes in pregnancy contribute to SUI. The gravid uterus applies pressure on the bladder and stretches the connective tissue and muscles that normally support the pelvic organs. In addition, increased progesterone levels relax the muscles responsible for maintaining urinary continence: the external urethral sphincter and pelvic floor muscles (levator ani muscle complex). Normally, the external urethral sphincter compresses the urethra and creates a high urethral closing pressure. The pelvic floor muscles usually stabilize the urethra against the anterior vaginal wall and contract to decrease the urethrovesical angle, thereby kinking the urethra closed.
Because of decreased urethral sphincter tone and pelvic floor muscle laxity, the compression and position/angle of the urethra are compromised such that sudden increases in intraabdominal pressure (eg, coughing, sneezing) can cause the pressure within the bladder to exceed the urethral closing pressure. This leads to intermittent leakage of urine.
(Choices A and C) Bladder outlet obstruction (eg, urethral compression by uterine fibroids) and impaired detrusor contractility (eg, spinal cord injury) both lead to urinary retention. In patients with urinary retention, urine slowly accumulates in the bladder until the intravesical pressure exceeds the urethral closing pressure, causing urine leakage. Because urine constantly accumulates in the bladder, patients have persistent involuntary dribbling of urine (overflow incontinence) rather than intermittent leakage with cough.
(Choice B) Detrusor muscle hyperactivity is the mechanism behind urgency incontinence (overactive bladder syndrome). Patients typically have an intense urge to urinate followed by an immediate, involuntary loss of urine.
(Choice E) During pregnancy, the sciatic nerve can become compressed due to increased joint laxity from circulating relaxin and changes in maternal posture (eg, spinal lordosis). Sciatica commonly presents as lower back pain radiating down one side of the hip to the leg. It does not cause urinary incontinence.
(Choice F) During pregnancy, the gravid uterus compresses the ureters, leading to physiologic hydronephrosis and ureteral dilation. These changes increase the risk for urinary stasis and urinary tract infection but do not cause incontinence.
Educational objective:
Stress urinary incontinence, the leakage of urine with increased intraabdominal pressure (eg, coughing), is common in pregnancy due to decreased external urethral sphincter tone and increased pelvic floor muscle laxity.