Serum and urine insulin-like growth factor-1 as biochemical growth maturity indicators I read with great interest articles published in the American Journal of Orthodontics and Dentofacial Orthopedics and would like to congratulate the authors of "Serum and urine insulin-like growth factor-1 as biochemical growth maturity indicators" (Sinha M, Tripathi T, Rai P, Gupta SK. Am J Orthod Dentofacial Orthop 2016;150:1020-7), who suggested a correlation and a noninvasive method for growth assessment without the restrictions involved in radiographic techniques. I would, however, like to bring attention to 1 important aspect of the study. It is reported that serum IGF-1 concentrations fluctuate during the menstrual cycle, with significantly greater values in the luteal phase compared with the follicular phase (Caufriez et al 1). The literature suggests controversial results about variations in the IGF-1 levels during the different phases of the menstrual cycle. 2 Since all the subjects included in the study were in the age group of 8 to 20 years, and sample testing was done randomly irrespective of the phase of the postpubertal female subjects, can the above-mentioned parameter have an influence on the results? Clarification will be greatly appreciated.