Pelvic ultrasound can observe the size and structure of internal genitalia in girls, and can be used for the diagnosis and differential diagnosis of CPP, especially when the results of the GnRH stimulation test are ambiguous (de Vries et al., 2006; Badouraki et al., 2008; de Vries and Phillip, 2011a; Wen et al., 2018), and the operation is simple, non-invasive and easy to be accepted by children and their parents (Ziereisen et al., 2005). This evidence concerns the gene GNRH1 and central precocious puberty.