The aim of this study is to determine whether plasma sclerostin levels is affected by sex hormones during menstrual cycle. Blood samples will be obtained at the beginning (between 2-5th day), mid (between 11-13th day) and end (between 21-23th day) of menstrual cycle. Serum sclerostin, estradiol, progesterone and testosteron levels will be measured blindly by only one investigator