Risk of ectopic pregnancy and duration of use of an intrauterine device.

A number of investigations have shown that accidental pregnancies occurring in long-term users of an intrauterine device (IUD) are more likely to be ectopic than those occurring in short-term users. An analysis of data collected in the Oxford-Family Planning Association contraceptive study, strongly suggests that the earlier findings are attributable to the progressive reduction in the frequency of intrauterine implantation with duration of IUD use. The absolute risk of ectopic pregnancy in IUD users was found to remain fairly constant with duration of use at about 1.2 per 1000 women per annum.