During the whole three menstrual cycle , record the length of each menstrual cycle , determine ovulation time by using basal body temperature and oviposit test paper , collect their morning urine samples at specified times ( the @th , @th , @th , @rd , @th , @th and @th day of first and the third menstrual cycle ; the @th , @th , @th , @th , @th , @nd , @th , @th , @st and @th day of the second menstrual cycle ) , determine the concentrations of estradiol , pregnanediol and creatinine in morning urine samples ; draw the curve of the concentration changing over time and calculate the area under the curve to the @th day .