A Cochrane review «»1 «S...»1 included 3 studies with a total of 695 subjects. In one trial comparing Copper intrauterine device (Cu-IUD) with expectant management there were fewer pregnancies in the IUD group (RR 0.09, 95% CI 0.03 to 0.26, n=300), which is in line with results from nonrandomised studies (3 pregnancies/3 470 women, failure rate 0.09%). There was no conclusive evidence of a difference in the risk of pregnancy between the Cu-IUD and mifepristone (RR 0.33, 95% CI 0.04 to 2.74; 2 RCTs, n = 395).
A meta-analysis «Cleland K, Zhu H, Goldstuck N et al. The efficacy ...»2 included 42 studies conducted in 6 countries (China, Egypt, Italy, the Netherlands, and the UK) between 1979 and 2011 and included 8 different types of IUD and 7034 women. The maximum timeframe from intercourse to insertion of the IUD ranged from 2 days to 10 or more days; the majority of insertions (74% of studies) occurred within 5 days of intercourse. The pregnancy rate was 0.09%. Altogether, there were 10 pregnancies, 6 pregnancies occurred among 5629 subjects in the studies conducted in China (failure rate = 0.11%; 95% CI = 0.05–0.23%) and 4 pregnancies occurred among 200 subjects in one study conducted in Egypt.
IUD is the only method to provide ongoing contraception if left in situ, and thus highly cost-effective.