The certainty of the evidence is downgraded by study quality (imbalance in baseline characteristics) and by imprecise results (very few outcome events).
In a multicentre trial «Turok DK, Gero A, Simmons RG et al. Levonorgestrel...»1 711 women (age 18- 35) who sought emergency contraception after at least one episode of unprotected intercourse within 5 days were randomly assigned in a 1:1 ratio to receive a levonorgestrel 52-mg IUD (LNG-IUD) or a copper T380A IUD. 655 women received assigned intervention. Of these, 590 participants had a 1-month urine pregnancy test. Participants were followed up 6 months. Pregnancy rates were 1 in 317 (0.3%; 95% CI 0.01 to 1.7) in the LNG-IUD group and 0 in 321 (0%; 95% CI 0 to 1.1) in the copper IUD group; the between-group absolute difference in both analyses was 0.3 percentage points (95% CI −0.9 to 1.8), consistent with the noninferiority of the LNG-IUD to the copper IUD. Adverse events resulting in participants seeking medical care in the first month occurred in 5.2% of in the LNG-IUD group and 4.9% of those in the copper IUD group.
A Cochrane review «Progestin intrauterine devices versus copper intrauterine devices for emergency contraception»1 «...»2 included one study, the above mentioned trial.