The objective is to test the hypothesis that luteal phase support with vaginal progesterone leads to a higher clinical pregnancy rate (primary outcome) and live birth rate (secondary outcome) when compared to no luteal phase support in a program of intrauterine insemination (IUI) after controlled ovarian stimulation with gonadotrophins. Additionally, the length of the luteal phase will be recorded (secondary outcome) in order to detect luteal phase defects/insufficiencies in the absence of luteal phase suppletion as well as luteal phase prolongation in case of luteal phase support which may be a burden for the patients waiting for the outcome of the treatment.

Inclusion Criteria:

Patients with an indication for IUI:

• unexplained infertility
• mild male factor infertility
• minimal-mild endometriosis

Women:

• first IUI cycle ever
• normal ovulatory cycles (26-32d)
• age<43,BMI≤30
• presence of at least one patent tube on hysterosalpingography and/or laparoscopy
• normal uterine cavity (ultrasound, hysterosalpingography, or laparoscopy)

Men: Total motile count ≥ 5 Million/ml after capacitation

Exclusion Criteria:

• Patients with contra-indication for pregnancy , infertility or progesterone use.