 All patients will undergo a full infertility investigation including hormonal evaluation between day 2 and day 5 of the cycle and confirmation of patency of the Fallopian tubes. Patients eligible for the study are between 18 and 40 years old, with regular menstrual cycles 21 - 35 days. Indications for the use of donor sperm are male factor infertility due to azoospermia or severe oligoasthenoteratozoospermia requiring donor sperm, the presence of a heritable genetic disorder in the male partner, a single-parent request or same-sex couples partners undergoing IUI. Exclusion criteria are the presence of tubal factor infertility, grade III endometriosis, more than 3 previous dIUI cycles, or patients in whom 3 follicles 14mm are observed during the cycle. The randomization procedure will take place the day the donor IUI procedure. The randomization will be performed on the IUI cycle level. Randomization into one of the two groups will be performed using an open computer-generated list. 