This is a prospective, randomized, controlled clinical trial designed to evaluate whether follicular flushing increases the number of cumulus-oocyte complexes (COCs) retrieved compared to single aspiration in patients with poor ovarian response belonging to Poseidon groups 3 and 4.

A total of 40 patients with poor ovarian response belonging to Poseidon groups 3 and 4 will be included. In each patient, one ovary will be randomized to the study technique (follicular flushing), and the other ovary will be randomized to the control technique (single aspiration).

This is a prospective, randomized, controlled clinical study designed to evaluate the effect of follicular flushing on the number of cumulus-oocyte complexes (COCs) retrieved, compared to single aspiration, in patients with poor ovarian response classified as Poseidon groups 3 and 4.

A total of 40 patients will be included. All participants will receive a standardized stimulation protocol consistent with current practice for patients diagnosed with low ovarian reserve. After meeting all inclusion criteria, controlled ovarian stimulation will begin within the first four days of the menstrual cycle, using an antagonist protocol in all cases.

Starting on the 6th day of ovarian stimulation, daily administration of a GnRH antagonist at a dose of 0.25 mg (Ganirelix® or Cetrorelix®) will be initiated. Final oocyte maturation will be triggered once at least one follicle reaches a diameter of ≥17 mm, using either 250 μg of recombinant hCG (Ovitrelle®; Merck Serono) or 0.2 mg of triptorelin acetate (Decapeptyl®), or a double trigger. Oocyte retrieval will be performed 36 hours after triggering final oocyte maturation.

On the day of oocyte retrieval, randomization will be performed using a computer-generated randomization list. In each patient, one ovary will be randomly assigned to the control group (single aspiration), and the contralateral ovary will be assigned to the study group (follicular flushing). Simple random allocation will be used. Each patient will be allowed to participate in the study only once.

Oocyte retrieval procedures will be performed by four trained physicians to evaluate the reproducibility and generalizability of the technique. Follicles will be aspirated using 17G needles in both groups. For follicular flushing, the same needle model used for single aspiration (Cook) will be employed. To eliminate dead space, the needle will be prefilled with flushing medium before beginning the procedure. Aspiration pressure will be maintained at 190 mmHg during oocyte retrieval.

In the single aspiration group, after aspirating all follicles, the needle will be rinsed with flushing medium to minimize the risk of oocyte retention inside the needle.

In the follicular flushing group, if no cumulus-oocyte complex (COC) is recovered during the initial aspiration, follicular flushing will be repeated until a COC is obtained, up to a maximum of three flushes. After three flushes, if no COC is retrieved, the procedure will be completed by rinsing with flushing medium to prevent possible oocyte retention within the needle.

The embryologist will immediately inform the physician performing the oocyte retrieval whether a COC has been recovered, in order to determine whether to continue flushing or proceed to the next follicle (open flushing technique).

The duration of the procedure will be recorded from needle insertion to its withdrawal for each ovary in both groups.

Inclusion Criteria:

• Pacientes con baja respuesta ovárica grupos POSEIDON 3 y 4 (< 35 años y RFA <5 y/o AMH < 1.2 ng/ml o > 35 años≥ 35 años y RFA <5 o AMH <1.2 ng/mL respectivamente)

  1. Pacientes menores o igual a 43 años.
  2. Índice de Masa Corporal (IMC) de 18-35 kg/m2
  3. Estimulación ovárica para ICSI
  4. Presencia y accesibilidad de ambos ovarios.
  5. Ausencia de patología ovárica
  6. Cuando se cumplan los criterios de desencadenamiento para la maduración final del ovocito, cada ovario debe contener al menos un folículo mayor o igual a 14 mm.
  7. Haber dado su consentimiento por escrito.

Exclusion Criteria:

• Presence of a single ovary.

Presence of ovarian pathology.

Use of conventional IVF as the fertilization method.