BEst Size for Ovulation Triggering in Poseidon 4 Patients (BEST 4 Study)

The timing of final oocyte maturation in assisted reproductive techniques is critically important. If serum steroid hormone levels are appropriate during the late follicular phase, ovulation triggering can be performed using various agents. There are numerous comparative studies in the literature on this topic.

However, a key issue is determining the most optimal timing for this trigger. In standard practice, the final triggering is performed when the follicle size reaches 17 mm or more.

The purpose of this is to obtain mature eggs from these follicles during the oocyte aspiration process.

However, in some special cases, to maximize the desired yield, this size threshold may be adjusted.

A prime example of this is in older patients with poor ovarian reserve, as the expected egg yield may not be achieved with standard practices.

During the oocyte collection process, fewer mature oocytes (M2) may be retrieved, or no oocytes may be retrieved at all, despite proper ovarian stimulation. Therefore, the optimal follicle size for these cases has not been definitively established in the literature. Thus, there is a need to determine other follicular thresholds specifically for older women with poor ovarian reserves to enhance egg and mature egg yields.

For this purpose, cases undergoing ovarian stimulation for assisted reproductive treatment and planned final oocyte triggering will be evaluated in two separate groups:

• **Experimental Group**: Final oocyte triggering will be performed when the follicle or follicles measure between 13-16 mm.
• **Control Group**: Final oocyte triggering will be performed when the follicle or follicles measure greater than 17 mm.

All triggers will be administered uniformly with 6500 units of recombinant hCG and 0,2 mg triptorelin injections.

The primary outcome of the study will be the number of mature oocytes. Secondary outcomes will include fertilization rates, embryo counts, and implantation rates.

Primary and secondary outcomes will be compared between the two groups.

Inclusion criteria

• Women age equal to or greater than 35 years
• Women with low serum AMH (<1,2 ng/ml),
• women with low AFC (<5)
• women Undergoing assisted reproduction with Short antagonist protocol or long -agonist protocol
• women who used Max daily gonadotropin dose of 300 IU

Exclusion criteria

• Age <35 years.
• Ovarian reserve parameters not meeting the POSEIDON group 4 definition.
• Natural or modified natural cycles without controlled ovarian stimulation.
• In vitro maturation (IVM) cycles.
• Luteal-phase stimulation or DuoStim protocols.
• Preimplantation genetic testing (PGT-A, PGT-M, or PGT-SR) cycles, unless prespecified for stratified analyses.
• Major untreated uterine cavity pathology (e.g., submucosal fibroids, significant intrauterine adhesions, congenital uterine anomalies) or untreated hydrosalpinx.
• Cycles with missing or incomplete follicular measurement data on the trigger day.
• Cycles with non-standardized or undocumented trigger-to-oocyte retrieval intervals.