The aim of the project is to investigate the effect of seminal plasma on the endometrium and to evaluate changes in the endometrial receptivity after exposure to seminal plasma. Implantation is still an important limiting factor for the improvement of pregnancy rate in the Assisted Reproductive Technology (ART). Usually, in fertility clinics, only the spermatozoa are used for the treatments while the rest of the seminal fluid is discarded. However, the importance of seminal fluid in fertility has gained interest in the last years but no conclusive that has been obtained yet. Experimental group: We decided to focus our attention on lesbian couples and single women undergoing ART procedures because they could benefice the most from this treatment since they usually do not have contact with seminal plasma. Moreover, to the best of our knowledge, they have more problems in achieving a pregnancy than heterosexual couples. Our observation is supported by a preliminary analysis of data from the Dansk fertilitetsselskab. Design Randomized, double-blinded, placebo-controlled study * Group 1 treated: 20 healthy lesbian or single women receiving assisted reproduction * Group 2 control: 20 healthy lesbian or single women receiving assisted reproduction Treatment * One month before the IVF procedure: First seminal plasma/placebo application during ovulation period * Same month of the IVF procedure: second seminal plasma/placebo application after ovum pick up 5 days after the first application an endometrial biopsy and one blood sample will be taken for analysis. Analysis: Endometrial transcriptome microarray analysis that will be verified through protein analysis. Differences in the transcriptome between the two groups will be compared with data in literature for an optimal endometrial receptivity. Moreover, clinical pregnancy rate and pregnancy outcome will be compared.