Levonorgestrel 52 mg intrauterine device (LNG-IUD) is a commonly used reversible form of long-acting contraception, which is also used for treatment of heavy menstrual bleeding (HMB) [1]. It is a T-shaped device, developed to best adapt to the triangular-shaped uterine cavity. Ideally the position of the shaft should be in the uterine cavity with the side arms extending from cornuum to cornuum. However, different malpositions have been described. With the improvement of the quality of the two-dimensional transvaginal ultrasound (2D-TVUS) in the last decades, better quality imaging is available. The shaft of the LNG-IUD in the uterine cavity can be visualized by 2D-TVUS, making most malpositions visible. The side arms can also be visualized by 2D-TVUS, but not in relation to the uterine cavity [2]. A three-dimensional TVUS (3D-TVUS) can render a coronal plane in which the localization of the side arms can be seen in relation to the cavity and the myometrium. When the side arms penetrate into the myometrium, this is called ‘embedment’. Due to the advantages of 3D techniques, embedment is assumed to be visualized by 3D-TVUS. However, it is unknown if 3D-TVUS is just a sonographic interpretation or truly represents embedment. To truly diagnose embedment a diagnostic hysteroscopy is needed.

In the literature, the question has been posed whether width of the uterine cavity is related to an increased risk of embedment of the side-arms of the LNG-IUD. One study produced evidence that IUDs should not be utilized in subjects with narrow uterine cavities [3]. In another study, participants with embedment of the side arms had a smaller fundal uterine cavity diameter [4]. Due to frequent complaints of intermenstrual bleeding or spotting with an LNG-IUD, it makes sense to look for a cause of the complaints. Because of the possibility of malposition or embedment, it is often a first step to perform an ultrasound. Before you decide to reposition or even remove the IUD, you need to know whether this embedment is actually the cause of these symptoms. This is why we started looking into whether embedment of the sidearms of the IUD does cause these complaints. There is little evidence whether embedment of the side arms is associated with unfavourable bleeding and/or pain. In a retrospective cohort investigation, abnormal location of the side arms was more often associated with pelvic pain and/or bleeding [5].

In this prospective study, we assessed the embedment of side arms with 3D-TVUS. The aim of this study was to evaluate the relation between embedment of side arms of the LNG-IUD in the myometrium and symptoms like bleeding and pain.