In a comparative use-effectiveness study, 855 Nova T and 883 TCu 200 Ag devices were inserted in a randomised sequence. By the end of the first year the gross rate of unplanned pregnancy was 1.1 per 100 users of Nova T and 2.1 per 100 users of TCu. After 2 years the pregnancy rates for Nova T and TCu were 3.1 and 4.8 per 100 users, respectively. Although there was no statistically significant difference between the rates for the two devices, they suggest a higher contraceptive efficacy for Nova T.
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Batár et al. (1987) studied this question.