There is a considerable concern about the effects of controlled ovarian hyperstimulation (COH) for In Vitro Fertilization- Embryo Transfer (IVF-ET) on embryo quality and on the incidence of chromosomal abnormalities in oocytes and embryos.

The main question remaining is if COH may increase the aneuploidies rate in young and healthy women. Therefore, the primary endpoint of the present study is to analyse the incidence of chromosomal abnormalities in this group of patients (oocyte donors), either in oocytes obtained after a natural cycle or in those retrieved after a COH cycle. To get rid of the male factor influence, donated sperm will be used.

Donor Inclusion Criteria:

• 18 to 35 years old.
• BMI: 18-25Kg/m2
• Regular menstrual cycles
• Normal kariotype
• No previous controlled ovarian hyperstimulation (COH) treatments.

Donor Exclusion Criteria:

• Endometriosis
• Policystic ovarian syndrome
• Recurrent miscarriages.

Recipient Inclusion Criteria

• Aged until 45 years old
• No systemic diseases
• Following egg and sperm donation treatment.

Recipient exclusion criteria:

• Uterine disease (polyps, myomas, mullerian defects)
• Recurrent miscarriages.