Objective:

To investigate the association of medium-size follicle proportions (MFP) on the trigger day with pregnancy outcomes in low prognosis patients undergoing GnRH antagonist protocol.

Approach:

• Study Design: Retrospective analysis of 1084 oocyte-retrieval cycles from 765 low prognosis patients based on POSEIDON criteria.
• MFP Definition: MFP defined as the ratio of follicles sized 13–18 mm to those ≥ 12 mm on trigger day.
• Group Division: Cycles divided into MFP < 70% and MFP ≥ 70% groups for comparison.
• Statistical Analysis: Multivariate logistic regression used to identify MFP as an independent predictor of live birth.

Key Findings:

• Live birth rate (LBR) was significantly lower in the MFP < 70% group (20.75%) compared to MFP ≥ 70% group (31.88%, P = 0.003).
• Significant differences in LBR were observed in both age groups: ≤ 35 years (28.18% vs 43.28%, P = 0.0148) and > 35 years (14.50% vs 23.66%, P = 0.0444).
• MFP < 70% group required a higher GnRH-antagonist dose (0.91 mg vs 0.78 mg, P < 0.0001) and longer duration (3.61 days vs 3.11 days, P < 0.0001).
• No significant difference in LBR was observed in frozen-thawed embryo transfer (FET) cycles.

Interpretation:

MFP is associated with live births in fresh transfers, highlighting the role of medium-sized follicle development in low prognosis patients.

Limitations:

• Retrospective design may introduce selection bias.
• Study focused only on fresh embryo transfer cycles; findings may not apply to all patient populations.

Conclusion:

Higher MFP is associated with improved live birth rates in fresh embryo transfers for low prognosis patients.