Pelvic inflammatory disease and the intrauterine device: findings in a large cohort study.

The incidence of pelvic inflammatory disease was investigated among parous women taking part in the Oxford-Family Planning Association contraceptive study. Hospital admission rates for "acute definite" disease were 1.51 per 1000 woman-years among those currently using an intrauterine device (IUD) and 0.14 per 1000 woman-years among those using other methods of birth control (age-standardised relative risk 10.5 to 1 with 95% confidence limits of 5.4 to 1 and 32 to 1). There was little evidence of an increased risk of such disease in ex-users of an IUD. Hospital admission for "chronic definite" disease, on the other hand, was commoner in ex-users of an IUD than in current users. Acute definite disease occurred somewhat more frequently during the early months of use of an IUD than during the later months. While the rate of such disease was increased in users of each type of device, the highest rate (8.1 per 1000 woman-years) was observed in users of the Dalkon shield. This rate, however, was based on only three affected women.