27 couples were recruited. This unexpected poor recruitment was due to more clinical pregnancies (for a better patients' selection) and more freeze-all cycles.

This randomized, controlled, prospective, crossover, open-label, two-treatments, two-period trial aimed to evaluate the preference expressed by the patient concerning the subcutaneous administration of progesterone versus the vaginal one.

The couples, scheduled for performing 2 In Vitro Fertilization (IVF)/Intracytoplasmic Sperm Injection (ICSI) cycles will be randomized to receive, as luteal phase supplementation, Pleyris 25 milligram (mg) (a single subcutaneous administration per day) or Prometrium 200 mg (3 vaginal administrations per day).

Each participant will receive both treatments. During the first IVF/ICSI cycle, the luteal phase will be supplemented with subcutaneous progesterone (S) or vaginal progesterone (V). At the end of the cycle (on the day of beta-hCG), a survey for determining the level of satisfaction will be administered and filled in by the patient during the waiting time and always before the knowledge of the result. This practical organization allows the elimination of emotional biases correlated with the outcome. In case of a negative beta-hCG, the patient will be scheduled for a second IVF/ICSI cycle after a washout (W) period (between 2 and 6 months). In the second cycle, the patient will undergo, during the luteal phase, the opposite treatment (V or S). Also in this case, the survey for evaluating the level of satisfaction will be administered on the day of beta-hCG, with the same modalities of the first cycle. The domains of the surveys are focused on facility of the administration, comfort, level of complaint, side effects, overall level of satisfaction.

The sequence S-V or V-S will be randomly assigned (random assignment) with the concealment of the allocation.

In case of a negative beta-hCG also in the second cycle, a post-hoc comparison between the two treatments will be carried out through a Semantic Differential Scale, in the "follow-up" phase.

Inclusion Criteria:

first IVF/ICSI attempt (at the enrolment), regular menstrual cycles (25-33 days), controlled ovarian stimulation performed with Gonadotropin Releasing Hormone (GnRH) antagonists and gonadotrophins (recombinant FSH)

Exclusion Criteria:

systemic diseases, chronic medical therapies, pregnancy in one of the IVF/ICSI cycles, embryo "freeze all" strategy in one of the IVF/ICSI cycles for preventing Ovarian Hyperstimulation Syndrome (OHSS)