'Key' precipitating event: first vaginal delivery may set stage for future incontinence.(Gynecology)

BALTIMORE -- The origin of stress incontinence can often be traced to injuries sustained during a woman's first vaginal delivery. Dr. Jacek Mostwin said at a urogynecology meeting sponsored by Johns Hopkins University.

"There's no end to which maternal injuries can contribute to stress incontinence. Studies have clearly shown that the first vaginal delivery is the key event in many subsequent episodes of stress incontinence," said Dr. Mostwin of the university.

Many internal support structures can be affected during labor and delivery, including the levator hiatus, which can become elongated; the levator muscles, which can tear and stretch; and the pudendal nerve, which can be directly compressed. Vaginal attachments can stretch to exceed the diameter of the baby's head, and the cardinal and uterosacral support structures and the urogenital diaphragm may stretch and tear beyond their ability to fully recover. Inadequate effacement and dilation of the cervix can cause the fetal head to push the cervix, stretching or tearing some of the cervical attachments. Even the size and shape of the pubis may cause paravaginal defects.

Paravaginal defects are associated with damage to the levator hiatus resulting from dilation and stretching. Tearing of connective tissue and widening of the levator hiatus may result. Once the levator hiatus is stretched and elongated, the location of the cervix may shift, making prolapse more likely. "Essentially, it's a hernia developing in the vaginal vault," Dr. Mostwin said. Certain types of prolapse are associated with stress incontinence. Stress-related prolapse can occur in either the upper third or lower third of the vagina, or a combined prolapse may occur, involving both segments.

Stress incontinence occurs if the urethra is directly affected, if the suburethral vaginal supports are affected, or if these two conditions occur simultaneously. These injuries tend to occur early in adulthood, ...