The aim of the present study is to prospectively evaluate whether performing an intra-uterine insemination 24 hours after the spontaneous LH peak may result in significantly higher ongoing pregnancy rates compared to 48 hours.

Inclusion Criteria:

• below 39 years of age on the day of LH peak
• donor semen
• natural cycle (without CC)
• cycle with less than 3 follicles reaching 15 mm of diameter or more.
• with basal hormonal values of progesterone ( < 1,2 ng/dl)

Exclusion Criteria:

The patients excluded are women

• who underwent more than 6 intrauterine inseminations,
• with tubal infertility