HealthDay News — Intrauterine devices (IUDs) are a highly effective form of emergency contraception, results of a meta-analysis indicate.

A review of 42 studies involving 7,034 women conducted between 1979 and 2011, revealed that 99.86% of those who had an IUD inserted after unprotected intercourse did not become pregnant, Kelly Cleland, MPHA, MPA, from Princeton University in New Jersey and colleagues reported in Human Reproduction.

“Because they are safe for the majority of women, highly effective and cost-effective when left in place as ongoing contraception, whenever clinically feasible, IUDs should be included in the range of emergency contraception options offered to patients presented after unprotected intercourse,” the researchers wrote.

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Nearly all of the IUDs included in the studies were copper-bearing, and the majority (74%) were inserted according to the current standard protocol of within 5 days of unprotected sex. Copper IUDs can be left in and will prevent pregnancy for up to 10 years after insertion.

Among the more than 7,000 postcoital IUD insertions, 10 pregnancies occurred, for an overall failure rate of 0.14% (95% CI: 0.08%-0.25%). Excluding one outlier study in which researchers purposely selected women at greater risk for pregnancy, the overall pregnancy rate was 0.09% (95% CI 0.04% to 0.19%), the researchers found.

Unintended pregnancies account for at least 36% of pregnancies worldwide and nearly half of pregnancies in the U.S., the researchers noted. The copper IUD could prove to be the most effective means of emergency contraception, followed by the currently popular oral ulipristal acetate (Ella or EllaOne; failure rate of about 1.4%) and levonorgestrel (Plan B; failure rate of about 2% to 3%).

But a lack of interest among health-care providers may pose a barrier to greater IUD emergency contraception use. A separate California study by Harper et al revealed that 85% of contraceptive providers in that state never suggested an IUD for emergency contraception, and 93% required at least two patient visits before insertion.

Limits of the current study include insufficient data on the delay between intercourse and insertion of the IUD, parity, cycle day of intercourse or IUD type to allow analysis by any of these variables, the researchers noted.

Cleland K et al. Hum Reprod. 2012; doi:10.1093/humrep/des140.

Harper CC et al. Obstet Gynecol 2012; 119: 220-226.