In Vitro Human Endometrial Cells and In Vivo Rat Model Studies Suggest That Ulipristal Acetate Impacts Endometrial Compatibility for Embryo Implantation.

BACKGROUND: Ulipristal acetate (UPA) and levonorgestrel are used as emergency hormonal contraceptives. Although both are highly effective in preventing pregnancy, UPA shows efficacy even when taken up to 120 h after unprotected sexual intercourse. AIMS: To investigate whether the mechanism of UPA's contraceptive action involves post-fertilization effects. METHODS: In vitro and in vivo studies using cultured human endometrial cells and a pre-clinical rat model. RESULTS: Endometrial cells treated with UPA showed changes in the expression of receptivity gene markers and a significant decrease in trophoblast spheroids attached to the cultured cells. In addition, administration of UPA to female unmated rats decreased the expression of implantation-related genes in the endometrium and inhibited the number of implantation sites in the mated group compared to the non-treated group. CONCLUSIONS: These results support that UPA as an emergency contraceptive might have post-fertilization effects that may affect embryo implantation.

Gene Expression Changes in the Ovary Mediate Non-Anovulatory Mechanisms of Contraception with Levonorgestrel.

BACKGROUND: Emergency contraception with levonorgestrel (LNG) is a viable option to prevent unintended pregnancies. Although the efficacy of LNG as an anovulatory agent decreases as treatment approaches ovulation, it still provides some contraceptive benefits. AIM: To better understand the contraceptive mechanisms of LNG in ovulatory subjects. METHODS: We conducted a study on Wistar rats that received a single dose of LNG (0.01 or 0.05 mg/kg) on the morning of proestrus before ovulation and evaluated its effects on ovarian gene expression, ovulation, and implantation. RESULTS: Our findings showed changes in the expression of genes involved in follicular development and oocyte quality. Pregnancy rates - as an indicator of ovulation - and embryo implantation were significantly lower than those in the control group. CONCLUSIONS: This study suggests that LNG alters regulatory factors in the ovary that are essential for the development of competent fertilizable oocytes, highlighting the non-anovulatory mechanisms by which levonorgestrel may regulate fertility and suggesting that it could be a novel observation that contributes to the understanding of emergency contraception in humans.