Urinary tract infection in relation to diaphragm use and obesity.

We have examined factors influencing the rate of first referral to hospital for urinary tract infection among the 17,032 women taking part in the Oxford Family Planning Association contraceptive study. The risk of first referral declined with age, was higher in nulliparous women than in parous women, was higher in non-obese than in obese women and was higher in current users of the diaphragm than in current users of other methods or no method of contraception. The main increase in the risk of referral in current diaphragm users occurred during the first 24 months when overall rates were 2-3 times higher in users than in non-users or ex-users of the diaphragm. The negative association between hospital referral for urinary tract infection and obesity was unexpected. It was not explicable in terms of age, parity or diaphragm use. It may be that obese women are less likely to receive trauma to the genital area during sexual intercourse than non-obese women because adipose tissue offers them some protection. Another possibility is that increased oestrogenization in obese women, resulting from peripheral conversion of androstenedione to oestrone, has a beneficial effect on the bladder and urethra, thus reducing the liability to infection.