Not all IUDs fit in young nulliparous and adolescent women.

Long-acting reversible contraceptive methods (LARC) are considered important to reduce the number of unintended pregnancies. Winner et al. found that women using oral contraceptives, a transdermal patch or a vaginal ring had a risk of contraceptive failure that was 20 times as high as the risk among those using LARC [intrauterine devices (IUDs), implants]. In the CHOICE cohort study of acceptance of LARC by young women, most subjects (∼70%) aged 18 years and older selected intrauterine contraception. However, many young women experience problems with IUD use, particularly if they are nulliparous. Researchers long ago demonstrated the great disparity between uterine cavities, particularly transverse dimensions, which were found to be on average only 2.5 cm in the fundal area in nulliparous women and only marginally wider in women who had given birth. Recent studies conducted in nulliparous women with conventional IUDs [e.g. Copper T380A or the Mirena intrauterine system (IUS)], which are 3.2 cm wide, came to the conclusion that side effects (e.g. bleeding, pain) are the consequence of disproportion between the IUD and the endometrial cavity and may lead to early discontinuation. 5 Other studies conducted in nulliparous women reported similar low continuation rates. A recent review article by the present author reports on randomised and nonrandomised studies conducted with the frameless GyneFix 200 and 330 IUDs in parous and nulliparous women. The unidimensional design of the frameless IUD explains its high acceptability and high continuation of use. Continuation rates exceeding 90% at 5 years are usual in such women. A recent multicentre study (unpublished data) conducted with the frameless copper and frameless levonorgestrel-releasing IUS in adolescent and young nulliparous women confirmed these high continuation rates. Figure 1 demonstrates the importance of an optimal IUD-cavity relationship. It is evident that high continuation of use is the aim of LARC and this can only be obtained if the acceptability of the method is high. The latter has been the challenge for researchers in recent decades.