The purpose of the present study is to assess the influence of the administration of low dose hCG on the endometrium. The study is a randomised trial where 2 groups of patients, undergoing a gonadotropin-releasing hormone antagonist protocol for in vitro fertilization, are studied. In addition to the histological findings, by analysing the correlation of the morphological pattern and gene expression profile of human endometrium on the day of oocyte retrieval in patients of both treatment groups, the investigators want to study the implantation potential.

Inclusion Criteria:

• < 36 years on day of randomisation
• FSH < 12 in the early follicular phase
• Normal ultrasound scan
• BMI between 18 and 29 (both inclusive)
• Randomisation at outpatient clinic

Exclusion Criteria:

• Endometriosis ≥ grade 3
• PCO syndrome
• Poor responder
• Endocrine or metabolic abnormalities