A thin endometrium is one of the most difficult problems encountered in assisted reproduction every day practice Regarding the proliferative phase, several ways of treatment have been undertaken to circumvent thin endometrium trying to increase thickness with questionable results.

The objective of the current study will be whether a daily dose of 150 IU (international units) of human chorionic gonadotropin (HCG) for seven days concomitant with estrogen administration in estrogen replacement cycles can increase the endometrial thickness and improve pregnancy outcome.

In this pilot study subjects with repeatedly resistant thin endometrium, less than 6mm, will be recruited. The investigators sought to investigate the possible role of adding low dose HCG in the follicular phase, on the endometrial growth and development. The investigators constructed this hypothesis based on the fact that LH/HCG (luteinizing hormone/human chorionic gonadotropin) receptor is present in endometrium and therefore a positive interaction could be anticipated when HCG is administered in the proliferative phase of endometrial growth. Furthermore, in a previous study, where human menopausal gonadotropin (hMG) -well known that renders its luteinizing hormone (LH) capacity due to low dose HCG contain- was compared to recombinant-follicular stimulating hormone (rec-FSH) during ovarian stimulation, endometrium was more likely to be iso-echogenic and hypo-echogenic in the hMG group, also anticipating a possible positive role of HCG activity.

Inclusion Criteria:

• (1) Less than 6mm endometrial thickness before, (2) at least two failed implantations before

Exclusion Criteria:

• Abnormal uterine cavity in Hysteroscopy