PID risk for IUD users highest in first 20 days after insertion; risk then falls sharply and remains low.
Researchers analyzed data on 22,908 women obtained from randomized WHO studies from 23 countries to determine whether the IUD increases the risk of pelvic inflammatory disease (PID). 35% of the women used the TCu220C IUD, 39% other copper releasing IUDs, 16% a hormonal IUD, and 9% the Lippes Loop. The overall PID incidence rate was 0.4% of all IUD insertions or 1.6 cases/1000 woman years. The incidence was greatest during the 1st 20 days after insertion (9.7 cases/1000 women years) and then declined to 1.4/1000 woman years. In fact, the risk of PID was >6 times greater within 20 days after insertion than it was >20 days after insertion. This high risk immediately after insertion was evident in every region where PID existed, at all insertion times, and in all age groups. The higher risk within the 20 days after insertion was attributed to contamination of the uterus during insertion. Women who had an IUD inserted after 1980 experienced PID 50% less often than those who had had it inserted earlier, e.g., the rate ratio for 1977-80 was 1.5 but was 0.5 for 1981-83 and 0.34 for 1984 and after. This may have been due to physicians being more aware of contraindications for IUD use, particularly past infection with sexually transmitted diseases )STDs). The rate ratio was higher in Africa (2.6) than it was in Europe (1) but lower in Asia (0.46) and in the Americas (0.39). None of the subjects in China experienced PID. Older women were at lower risk of PID than 15-24 year olds (0.44 for 25-29 year olds, 0.38 for 30-34 year olds, and 0.35 for =or> 35 year olds). The researchers believed the higher risk life styles of the younger group accounted for this difference. Risk of PID decreased with family size (2.5 for 0 children, 0.56 for 2 children, and 0.39 for at least 4 children). The risk of PID did not differ with IUD type. The researchers concluded that the major determinant of PID is exposure to an STD rather than type of IUD.