Reply: non-significant results do not imply similarity or safety in NC-FET follicle-size comparisons: a clarification

Dear Editor, We would like to thank Dr Iga for his thoughtful and constructive comments (Iga, 2026) on our article ‘Pregnancy and perinatal outcomes after modified natural cycle-frozen embryo transfers according to size of the dominant follicle on the hCG trigger day’. (Zhang et al, 2025). We appreciate his interest in our work and the opportunity to clarify several aspects of our study. First, our study (Zhang et al, 2025) employed a retrospective design rather than a non-inferiority trial. Accordingly, our conclusions focused on the absence of a statistically significant difference. Although non-significance does not prove equivalence, pregnancy rates were similar, and adjusted analyses showed that no significant differences were observed in any of the pregnancy outcomes when comparing the reference group to the other follicle size categories. Moreover, when treating follicle size as a continuous variable, there remained no significant association between the follicle size and any reproductive outcomes. Additionally, several sensitivity analyses have been conducted, and the results are consistent with the main findings. Second, we acknowledge that the sample sizes in certain subgroups, particularly for the