Levonorgestrel emergency contraception : Effects on endometrial development and embryo implantation

Abstract: Background: The dialog between the developing embryo and receptive endometrium is under the control of ovarian steroids and numerous biomolecules, some of which have been suggested as markers of endometrial receptivity . Unintended pregnancies are common. The standard treatment with levonorgestrel (LNG, 1.5mg either in a single dose or in two does with 12 hours intervals) provides women with a safe means of preventing unwanted pregnancy after unprotected intercourse. However, its mechanisms of action when used for emergency contraception (EC) remain a matter of discussion. Overall aim: To study the effects of LNG used for EC on markers of endometrial receptivity, embryo implantation and first-trimester tissues. Papers I and II: Endometrial biopsies were taken from fertil women with a regular menstrual cycle (n=12 for paper I; n=22 for paper II) during cycle days LH+4 to LH+5. The stromal and epithelial cells were isolated and cocultured in 3-dimensional endometrial constructs. Immunostaining of estrogen receptor (ER)-α and β, progesterone receptor (PR)- (A+B), vascular endothelial growth factor (VEGF), leukemia inhibitory factor (LIF), interleukin (IL)-1β, and cyclooxygenase (COX)-2 were present in both cultured epithelial and stromals cells, whereas the expression of PR-B, androgen receptor (AR), integrin αvβ3, and mucin 1 were confined to epithelial cells. Treatment with LNG did not change the expression of any markers studied or impair blastocyst attachment to the endometrial construct. Mifepristone, used as a positive control, up-regulated the ER-β and PR-B expression, whereas it down-regulated the expression of stromal VEGF, epithelial integrin αvβ3 and mucin 1. Mifepristone also inhibited blastocyst attachment in vitro. Paper III: First-trimester decidua and chorionic villi were collected from women (n=9) who had self-administered LNG (1.5mg) for EC after ovulation and subsequently became pregnant and who opted to interrupt the pregnancy with vacuum aspiration. Samples from comparable, unexposed women (n=9) were collected as controls. No significant differences in the expression of ERs, PRs, AR or Ki67 in the samples exposed and unexposed to LNG were seen using immunohistochemistry. Paper IV: Endometrial biopsies were taken from fertil women (n=8) on cycle days LH+6 to LH+8: i) throughout the normal cycle and ii) after treatment with LNG (0.75mg daily during LH+1 to LH+4). The treatment significantly reduced PR-A and PR-B immunoreactivity in glandular epithelium, whereas it increased LIF stromal immunoreactivity and mRNA expression. Differences in the expression of other markers of endometrial receptivity were insignificant between the two groups. Conclusions: Levonorgestrel used for EC does not affect markers of endometrial receptivity studied neither in vitro nor in vivo. Levonorgestrel does not impair embryo attachment to a 3-D endometrial cell culture construct. Post-ovulatory administration of LNG has no effect on the expression of ovarian steroid recpetors or Ki67 in first-trimester tissues. New agents with improved effects on follicular development, ovulation and endometrial receptivity should be developed and available to increase the EC efficacy.