Medium-sized follicle proportion on the trigger day may be associated with higher live birth rate in fresh embryo transfer cycles among low-prognosis patients: a retrospective cohort study.

OBJECTIVE

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

MATERIALS AND

METHODS

A total of 1084 oocyte-retrieval cycles from 765 patients diagnosed with low prognosis according to POSEIDON criteria were enrolled in this retrospective study between January 2017 and December 2023. MFP was defined as ratio of the number of follicles sized 13-18 mm to the number of follicles ≥ 12 mm on trigger day. According to the value of MFP, cycles were divided into MFP < 70% and MFP ≥ 70% groups. Cycle characteristics, laboratory data and pregnancy outcomes were compared between the two groups. Multivariate logistic regression analysis was used to identify whether the value of MFP was independent predictor of live birth.

RESULTS

The live birth rate (LBR) (20.75% vs 31.88%, P = 0.003) in fresh embryo transfer cycles was significantly lower in the MFP < 70% group than in the MFP ≥ 70% group. This difference was observed both in patients aged ≤ 35 years (28.18% vs 43.28%, P = 0.0148) and > 35 years (14.50% vs 23.66%, P = 0.0444). A significant increase in GnRH-antagonist dose (0.91 ± 0.44 mg vs 0.78 ± 0.43 mg, P < 0.0001) and duration (3.61 ± 1.57 days vs 3.11 ± 1.55 days, P < 0.0001) was observed in MFP < 70% group. No significant difference was observed in the LBR between groups in frozen-thawed embryo transfer (FET) cycles. Multivariate logistic regression analysis showed that the value of MFP was positively associated with live births in fresh transfers whether MFP was modeled as a continuous variable (per 1% increase) or as a binary threshold (≥ 70% vs. < 70%).

CONCLUSIONS

These findings highlight the significant association of MFP with LBR in fresh transfer cycles, suggesting that more attention should be paid to medium-sized follicle development when determining the timing of trigger and embryo transfer strategies for low prognosis patients. No significant association was observed in FET cycles, suggesting that the benefit of higher MFP may be specific to fresh transfer.