P18 Human endometrial stroma following exposure to the levonorgestrel intrauterine system (LNG-IUS).

The levonorgestrel intrauterine system (LNG-IUS or Mirena®) is an efficient contraceptive device which also brings about a profound reduction in menstrual blood loss. It is therefore a recognised treatment for menorrhagia. A common cause of discontinuation of treatment is the associated breakthrough bleeding which occurs in the early phase of use. Stereological methods were employed to document stromal morphology in women treated with LNG-IUS prior to hysterectomy. The results were compared with data obtained from biopsies taken from untreated women at various stages of the menstrual cycle (Dockery et al. Human Reproduction 4, 1998). All patients provided written informed consent. Endometrial stroma was examined in 2 groups of women: hysterectomy samples from women exposed to LNG-IUS for 6 to 10 wk (n = 7), and well timed normal luteal phase biopsy specimens taken 2, 4, 6, 8,10 and 12 d after the luteinising hormone (LH) surge (n = 4 or 5 on each day). A number of morphological parameters were estimated including nuclear volume and the volume weighted star volume using the digital stereology programme, Kinetic Imaging Sterelogy (Kinetic Imaging Ltd.) Previously we have shown, that there was little overall difference in the ultrastructure of endothelial cells in the LNG-IUS group compared with the control group (Treacy et al. J. Anat, 200, 2002). The vascular basal lamina was thinner in the LNG-IUS group and there was also a borderline significant reduction in vessel wall thickness compared with the controls. In the present study the star volume of the stromal extracellular space in the LNG-IUS group was significantly smaller than that of the control group on all days of the menstrual cycle studied (P < 0.05). The volume weighted mean (± SE) star volume at LH+2 was 60067 ± 8004 µm3 rising to a maximum of 64574 ± 7978 µm3 at LH+10, whereas the value for the LNG-IUS group was 17548 ± 4272 µm3. This is consistent with the decidual transformation of the stroma in the LNG-IUS group. These changes in vessel wall thickness and alterations in the stroma into which the vessels are embedded may be responsible for some of the breakthrough bleeding seen after short- term exposure to intrauterine LNG. We acknowledge support from Schering Healthcare UK.