Controlled Ovarian Stimulation Versus Modified Natural Cycles in Poor Responders

Inclusion Criteria: * Informed consent form (ICF) dated and signed. * Age ≥18 and \<45 years old. * Body Mass Index (BMI) ≥18.5 Kg/m² and \<35 Kg/m². * Regular menstrual cycles (between 21 and 35 days). * Two ovaries present. * Current pregnancy wish. * Poor responders as defined according to the POSEIDON criteria: POSEIDON Group 3: patients \< 35 years with poor ovarian reserve pre-stimulation parameters (AFC \<5 or AMH \<1.2 ng/mL); POSEIDON Group 4: patients ≥35 years with poor ovarian reserve pre-stimulation parameters (AFC \<5 or AMH \<1.2 ng/mL). Exclusion Criteria: * Simultaneous participation in another clinical study. * Untreated and uncontrolled thyroid dysfunction. * Tumors of the ovary, breast, uterus, pituitary or hypothalamus. * Abnormal (not menstrual) vaginal bleeding without a known/diagnosed cause. * Ovarian cysts or enlarged ovaries. * Malformations of the reproductive organs. * Current use of oral contraceptives, anti-psychotics, anti-epileptics or chemotherapy. * Previous antibiotic hypersensitivity reactions (streptomycin and/or neomycin). * Patients who undergo preimplantation genetic testing (PGT), fertility preservation or oocyte donation.