在卡罗威等所做的一项严格控制氮平衡的研究中,月经期每日尿中排泄的尿素氮类似一双相的正弦波曲线。尿中的尿素氮在卵泡中期和黄体中期达最高,在月经期和排卵期最低。但这一研究没有测定卵巢激素浓度,因而月经周期各阶段的划分不是很准确,在这一类的研究 In a study conducted by Carowell et al., Which strictly controls nitrogen balance, the urea nitrogen excreted in the urine during menstruation resembles a sinusoidal curve of a biphasic phase. Urea nitrogen in urine in mid-follicle and mid-luteal up to the highest, in the menstrual period and minimum ovulation. However, this study did not determine the concentration of ovarian hormone, so the division of the menstrual cycle is not very accurate, in this type of study