Abstract Background:

Levonorgestrel (LNG) is a progesterone receptor agonist used in both regular and emergency hormonal contraception; however, its effects on the endometrium as a contraceptive remain widely unknown and under public debate.

Objective:

To analyze the effects of LNG or mifepristone (MFP), a progesterone receptor antagonist and also known as RU-486, administered at the time of follicle rupture (FR) on endometrial transcriptome during the receptive period of the menstrual cycle.

Methods:

Ten volunteers ovulatory women were studied during two menstrual cycles, a control cycle and a consecutively treated cycle; in this last case, women were randomly allocated to two groups of 5 women each, receiving one dose of LNG (1.5 mg) or MFP (50 mg) the day of the FR by ultrasound. Endometrial biopsies were taken 6 days after drug administration and prepared for microarray analysis.

Results:

Genomic functional analysis in the LNG-treated group showed as activated the bio-functions embryo implantation and decidualization, while these bio-functions in the T-MFP group were predicted as inhibited.

Conclusions:

The administration of LNG as a hormonal emergency contraceptive resulted in an endometrial gene expression profile associated with receptivity. These results agree on the concept that LNG does not affect endometrial receptivity and/or embryo implantation when used as an emergency contraceptive.