Related Experiment Video
Updated: Jun 20, 2026

Nerve-sparing Mid-urethral Obstruction (NeMO) in Female Small Rodents
Published on: April 25, 2017
Change in urethral sphincter neuromuscular function during pregnancy persists after delivery
Alison C Weidner1, Mary M T South, Donald B Sanders
1Department of Obstetrics and Gynecology, Duke University Medical Center, Durham, NC, USA.
Objective:
The purpose of this study was to assess the effect of pregnancy and first vaginal delivery on urethral striated sphincter neuromuscular function.
Study Design:
Quantitative electromyographic (EMG) interference pattern analysis of the urethral sphincter of 23 nulligravidas and 31 third trimester primigravidas allowed comparison of mean motor unit parameters before term vaginal delivery and postpartum.
Results:
Mean electromyographic interference pattern parameters in the primigravidas were significantly lower than nulligravidas even antepartum, with decreased turns, lower amplitude, and less activity. The only significant change at 6 months' postpartum was further decline in number of turns resulting in a further decrease in turns:amplitude. All other electromyographic abnormalities persisted at 6 months' postpartum and remained abnormal compared to the nulligravidas.
Conclusion:
Urethral sphincter neuromuscular function changed significantly during pregnancy and these changes persisted postpartum. Lack of recovery 6 months' postpartum suggests a physiologic impact of pregnancy itself on future risk of urinary incontinence.
Related Concept Videos
The Micturition Reflex
The process begins with bladder filling, where the bladder wall stretches as urine accumulates. This stretching activates the urine storage reflex, mediated by the sacral spinal segments and the pontine storage center. Efferent sympathetic impulses stimulate the detrusor muscle to relax and the internal urethral sphincter to contract, facilitating urine...
Anatomy of the Genitourinary System II: Bladder and Urethra
Microbiota of the Urogenital Tract
Muscles of the Pelvic Floor and Perineum
Perineal Layer
The perineum is a diamond-shaped area below the pelvic diaphragm, divided into an anterior urogenital triangle that contains the external genitals and a posterior anal triangle housing the anus. The urogenital...
Urethra
The anatomy of the urethra differs between males and females. In females, the urethra is short, measuring about 3–4 cm in length, and opens anterior to the vaginal opening. In males, the urethra is longer and passes through the penis, serving dual purposes: expelling urine and ejaculating semen. The male urethra is...
Mitral Valve Prolapse III: Nursing Management
