HONG KONG, Oct 26 (Reuters) - Women who have undergone hysterectomy, or removal of the womb, are at higher risk of urinary incontinence that needs to be corrected by surgery later on, a 30-year Swedish study has found.

The risk is especially high for women who have given birth to more than one child vaginally, the researchers wrote in the latest issue of The Lancet journal, urging more caution.

"Women should be counselled about associated long-term risks related to hysterectomy, and other therapeutic options should be considered before radical methods of treatment," they wrote.

Hysterectomy is the removal of the uterus, or womb, and it may be partial or complete. It is carried out to remove cancers of the reproductive system, postmenopausal bleeding, collapse of the uterus or uterine prolapse, and some other disorders.

Seen as a definitive cure to such disorders, it has become very common. One in five British women will have undergone a hysterectomy by age 55.

In the United States, 600,000 hysterectomies are undertaken each year, of which 90 percent are done for benign reasons, or non-cancer and other non-life-threatening conditions.

Between 1973 and 2003, researchers in Sweden tracked 165,260 women who had undergone hysterectomies and compared them to 479,506 other women who had not had the procedure.

They found the risk of undergoing stress urinary incontinence surgery (SUIS) was 2.4 times higher in the hysterectomy group than the control group.

"The highest overall risk was within five years of hysterectomy, when patients in the exposed group were 2.7 times more likely than those in the unexposed group to require SUIS. The lowest risk was seen in patients more than 10 years after hysterectomy, when the risk was 2.1 times higher for exposed patients," they said.

The worst were women who had had four or more vaginal births, who faced a 16-fold higher risk of undergoing SUIS.

The authors believe hysterectomies may interfere with the complex workings of the urethra, the tube connecting the urinary bladder to the outside of the body.

"The most biologically plausible rationale for this association is surgical trauma caused when the uterus and cervix are severed from pelvic-floor supportive tissues at the time of hysterectomy," they wrote.

"Hysterectomy could interfere with the intricate urethral sphincter mechanism ... it might also result in changes of urethral and bladder neck support."

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