To prospectively determine the most appropriate inseminated volume in donor IUI cycles. It is hypothesized that if the procedure is performed with 0.5 mL instead of 0.2, higher clinical pregnancy rates will be achieved by promoting higher sperm densities in the fallopian tubes at the time of ovulation by decreasing the amount of sperm cells lost during preparation and handling.

A prospective RCT will be performed, including patients undergoing dIUI under ovulation induction. The trial is established to compare two inseminated volumes, 0.2 ml (control group) and 0.5 mL (study group), and will be conducted at the Reproductive Medicine Service of the Dexeus Women's Health Center. The Institutional Review Board has approved the research project and an informed consent will be obtained from all patients participating to the study.

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.

IUI will be performed with a Wallace® catheter depositing 0.2 or 0.5 ml of the sperm sample at the uterine fundus. All IUIs will be performed between 12 p.m. and 4 pm. After the procedure, 10 min of bed rest will be prescribed. Inseminations will be performed every day of the week, including weekends.

Inclusion Criteria:

• 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 and with regular menstrual cycles (21 - 35 days). Indications for the use of donor sperm are severe male factor infertility 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-IV endometriosis, more than 3 previous failed dIUI cycles, or patients in whom ≥3 follicles >14mm are observed during the IUI cycle. Patients will be included in the study only once. The randomization will be performed on the IUI cycle level. The group allocation will take place the day the dIUI and the biologist will randomized all included patients into one of the two groups using an open computer-generated list.