Why does urinary incontinence mostly affect women?
As we have seen, incontinence is a condition that can affect anyone. However, there are several reasons why women are particularly prone to it.
Pregnancy
In pregnancy, the body’s systems adapt to provide for the fetus as well as the mother. The bladder and pelvis undergo several changes during this time.
One of the first effects of pregnancy is to increase the amount of urine produced by the kidneys. This results very early on in an increase in the frequency of passing urine. Other hormonal effects lead to a general relaxation of the tissues in the pelvis, allowing the pelvis to become more flexible during the pregnancy and birth. The bladder may not empty as well during pregnancy as a result of the pressure effects. These changes may reduce the natural barriers to bacteria which can lead to an increased occurrence of urinary tract infections.
As the uterus enlarges, increased pressure on the bladder leads to a need to pass urine more frequently. In about a third of women this increased pressure leads to leakage. This leakage usually stops with the birth of the baby, and is not linked to incontinence after childbirth.
Pregnancy can also lead to damage to the nerves controlling the muscles in the pelvis. In some women, the damage appears not to heal and this may be one of the causes of subsequent problems.
Childbirth and breast-feeding
Childbirth itself can damage the muscles and supporting structures in the pelvis. During a vaginal delivery there is stretching of the side walls of the vagina and of the muscles of the pelvic floor. These muscles and tissues may not recover completely and this can cause loss of support for the uterus (womb) and the bladder neck, which may eventually lead to prolapse of the uterus.
As the baby descends through the birth canal, damage may be caused to a nerve called the pudendal nerve, which controls the muscles of the pelvic floor and runs around the edge of the birth canal; this may lead to incontinence.
Breast-feeding helps to burn off the excess weight put on during pregnancy; it also helps pass on important nutrition and antibodies to the baby. Breast-feeding also delays the return of normal periods. This is sometimes relied on as a form of contraception, in that the chances of conceiving while breast-feeding are reduced because ovulation is less likely to occur, but it is not a reliable means of birth control.
This delay in return to normal function of the ovary also means that the amount of oestrogen circulating is less. The reduction in circulating oestrogen may mean that it takes longer for the pelvis to recover from any damage as the tissues in the pelvis are sensitive to the hormone oestrogen.
At the present time, there is no way to predict accurately which women are at risk of developing incontinence after childbirth. Various factors that may influence the effect of childbirth on your pelvis include the number of children that you have had, the type of delivery you had, how much the babies weighed, how long you were in labour and how long you pushed for.
The first vaginal delivery carries the greatest risk, but even with this most women have no long-term symptoms. Instrumental deliveries (by forceps and Ventouse) do carry a higher risk than normal deliveries. Caesarean section seems to spare some of these effects, but the benefit is lost after repeated pregnancies.
Something that does seem to be effective in minimising the risk of incontinence after childbirth is using pelvic floor exercises (see ‘Finding out what’s wrong’). These need to be taught properly and practised frequently. Most doctors feel that doing pelvic floor exercises before delivery may help to prevent symptoms. They need to be continued long term afterwards to be totally effective.
The menopause
At the menopause the ovaries cease to function and oestrogen levels in the blood fall dramatically. This can be responsible for the symptoms commonly associated with the menopause such as hot flushes and night sweats. It also has an effect on the pelvic tissues, which are sensitive to oestrogen.
As oestrogen levels drop, the muscles and tissues in the pelvis thin and lose some of their previous strength. This particularly affects collagen, which is a supporting protein, in the skin. This results in loss of support for pelvic organs such as the bladder, bowel and womb, and may eventually cause vaginal prolapse.
Treatment with hormone replacement therapy (HRT) may help to reverse these changes, but will not cure the problem, because once the collagen has weakened it will never totally go back to its former strength.
One other long-term effect of low oestrogen is atrophic vaginitis, which is a condition in which the vaginal walls become thin and inflamed. This results in itching and soreness. Atrophic vaginitis may be associated with changes in the bacteria within the vagina. The vaginal discomfort may lead to irritation around the urethra and so to increased frequency of passing urine.
Increased likelihood of infections
The pelvic anatomy of women increases the likelihood of bladder infections, because the passage between the bladder and the outside, the urethra, is relatively short. This makes it easier for bacteria to enter the bladder. Sex may also help bacteria get into the bladder by pushing them upwards during intercourse.
KEY POINTS
- Women are particularly prone to incontinence
- Hormonal changes in pregnancy and the menopause can cause problems
- Physical damage to nerves and tissues may occur during childbirth
- The pelvic anatomy of women increases the likelihood of bladder infections compared with men
