Ectopic pregnancy and IUDs; incidence, risk rate and predisposing factors.

During a period of 4 years, 1974-77, in Uppsala county; Sweden, 203 women underwent surgery for ectopic pregnancy with histological proof of the diagnosis. For the female population of fertile age this corresponds to 0.11 ectopics per 100 women 15-44 years of age, or 1.08 per 100 notified pregnancies, or 1.53 per 100 births. Fifty-five of the women with ectopic pregnancy were using an intrauterine device (IUD) (48 a copper-bearing IUD and 7 some other type of device), and 6 women used a low dose progestogen contraceptive. For users of copper-bearing IUDs the risk of an ectopic pregnancy was estimated to be 0.15 per 100 women years. When comparing this latter risk rate with the overall incidence rate of 0.11, it must be observed that the populations forming the denominator in these two rates differ with respect to some crucial characteristics. Nulliparity and predisposing factors were found statistically significantly more often in non-IUD-users with an ectopic pregnancy than in IUD-users. Such predisposing factors may be less prevalent in IUD-users, as in other populations. This may explain why ectopic pregnancy has been found to occur less frequently than theoretically expected among IUD-users. The "ectopic preventing" capacity of the IUD may therefore be considerably lower than has been previously claimed.