To the Editor:

We read the excellent original study by Rogenhofer et al. [1]. They conducted a study recruiting 469 women to investigate 3-month quartile D3 fluctuations and the impact on anti-Muellerian hormone (AMH) and Assisted Reproductive Technologies (ART) outcome. They concluded that AMH was affected by season, and the peak of AMH was in autumn from August to the end of October, and the fertilization rate and total number of collected oocytes were positively correlated with D3 serum concentration. We would like to thank Rogenhofer et. al for their dedication to the preparation for the couples who need ART to reproductive. Nevertheless, we put forward the following suggestion that may strengthen the rigor of the results in this article.

As the authors described in the “ART procedure” section, “Data and measurements were evaluated in 3-month quartiles (1st August–31st October, 1st November–31st January, 1st February–30th April, 1st May–31st July) and impact on ART outcome was assessed. ” and we can speculate that repeated measurement of variance analysis should be utilized [2]. Technically, repeated measurement of variance analysis should be performed if a variable is measured 3 times or >3 times. Furthermore, repeated measurement of variance analysis considers the effect of time factor (1st August–31st October, 1st November–31st January, 1st February–30th April, 1st May–31st July) on the result. However, repeated measurement of variance analysis was not mentioned in this study, which impair the reliability of data analysis. If the repeated measurement of variance analysis had been applied, the results of this study might be more consistent with the actual one.