Differential optimal follicle sizes for ovulatory dysfunction and unexplained infertility

1. Among patients with ovulatory dysfunction, dominant follicles measuring 17–18.9 mm were associated with poorer pregnancy outcomes compared to follicles ≥ 19 mm.

2. Among patients with unexplained infertility, dominant follicles > 21 mm were associated with a lower positive HCG rate compared to follicles measuring 17–21 mm.

Evidence Rating Level: 2 (Good)

Intrauterine insemination with ovulation induction (OI-IUI) is a widely used fertility treatment. Letrozole (LE), a third-generation aromatase inhibitor, is a commonly used medication for ovulation induction. However, research on the optimal dominant follicle size for triggering ovulation in LE-IUI cycles remains limited and inconclusive. This study thus aimed to determine the optimal dominant follicle size on the trigger day in patients with ovulatory dysfunction (OD) and unexplained infertility (UI) undergoing intrauterine insemination with letrozole (LE-IUI) cycles. This retrospective study included females under 40 years of age with OD or UI who underwent LE-IUI at a reproductive medicine center in Guangzhou, China. Participants were propensity matched 1:1 for baseline characteristics. Out of the 693 cycles of OD and 580 cycles of UI initially screened for this study, 411 cycles of each group were analyzed after propensity matching (OD: mean [SD] age, 31.02 [3.44]; UI: mean [SD] age, 31.20 [3.43]). Compared to the UI group, the OD group had higher rates of human chorionic gonadotropin (HCG) positive (22.4% vs. 9.5%), clinical pregnancy (21.5% vs. 7.9%), and live birth (19% vs. 7.1%) (P < 0.001 for all). In the OD group, patients with dominant follicle size 17–18.9 mm had lower rates of HCG positive, clinical pregnancy, and live birth compared to those with dominant follicle size 19–21.0 mm and > 21.0 mm (HCG positive: 7.6% vs. 21.5% vs. 26.2%; clinical pregnancy: 6.1% vs. 21.5% vs. 25.6%, live birth: 4.5% vs. 19.2% vs. 23.2%; P < 0.05 for all). Conversely, in the UI group, those with dominant follicle size > 21.0 mm had lower HCG positive rates (13.3% vs. 11.8% vs. 3.4%, P = 0.023) compared to those with dominant follicle size 17–18.9 mm and 19–21.0 mm. Overall, study results suggest that the optimal dominant follicle size for triggering ovulation is ≥ 19.0 mm for patients with ovulatory dysfunction, while a size ≤ 21 mm may improve HCG positive rates for patients with unexplained infertility. These findings highlight the importance of considering the underlying cause of infertility when determining trigger timing. Future randomized control trials are needed to validate study findings.

Click to read the study in European Journal of Medical Research

Image: PD

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