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The menstrual cycle of fertile female is regulated by multiple organs and hormones, controlling the reproductive health and fertility of females. This paper is dedicated to exploring how two negative feedback loops regulate and influence the dynamic behavior of the menstrual cycle. We simplified the regulation circuit of the menstrual cycle into a nonlinear differential equation with two time delays. This simplified mathematical model integrates the hypothalamus–pituitary–ovary primary negative feedback loop and the negative feedback auxiliary loop between the ovary and the pituitary. We investigated the delay-dependent conditions for the stability of the model’s equilibrium points and also demonstrated the presence of Hopf bifurcations. Theoretical analysis suggests that the primary feedback loop is the major factor driving oscillation in the system. Further numerical simulations indicate that the negative feedback auxiliary loop allows the system to adjust its amplitude while maintaining the robustness of the cycle length. Consequently, the results obtained from this model provide new insights into the regulation of oscillations in menstrual cycle irregularities.

The effect of Tokishakuyakusan, a Chinese herbal medicine, was examined, in vivo, in women with luteal insufficiency and in women with normal menstrual cycles. Luteal insufficiency was determined by daily measurement of basal body temperature and plasma progesterone levels. Tokishakuyakusan improved luteal insufficiency. Furthermore, the effects of Tokishakuyakusan on prolactin, gonadotropins, steroids, angiotensin II, ANP and renin levels in the blood of women with normal menstrual cycles were studied, as were the medicine's effects on estrogens, pregnenediol and LH in the urine of the same women. Tokishakuyakusan had no adverse effect on hormonal levels in either blood or urine. Furthermore, no clinical side effects were detected. These results suggest that Tokishakuyakusan improves luteal insufficiency in women but does not affect the hormonal levels of women with normal menstrual cycles.

Several Chinese herbal medicine textbooks describe that a short menstrual cycle indicates "Yang" status and a long cycle indicates "Yin" status. However, we sometimes encounter Yang patients with a long cycle or Yin patients with a short cycle in daily practice. Therefore, we reviewed the relationship between Yin-Yang and length of menstrual cycle. A questionnaire addressing both menstrual cycle and several parameters for determining Yin-Yang was completed at the time of the patients' visit to the hospital. Patients were divided into Yang or Yin groups, and menstrual cycle was compared between the two groups. A short menstrual cycle was mostly observed in Yin patients (27.42 ± 1.73, 95% CI: 26.32 ~ 28.52, n = 12) and a long cycle was mostly observed in Yang patients (31.63 ± 3.96, 95% C.I: 29.51 ~ 33.74, n = 16). The difference in menstrual cycle between the two groups was significant (p = 0.002), and this result was entirely opposite to the traditional theory. This study identified a discrepancy between the traditional theory and the actual menstrual cycle findings in this small population. Current reexamination of the relationship between Yin-Yang and menstruation in a larger population is warranted.

The matched wavelet is designed in this paper using an improved genetic algorithm for detecting the Heart Rate Variability (HRV) variations within phases of the menstrual cycle accurately. The idea of an improved genetic algorithm is to use an optimization technique like least mean square (LMS) before the genetic algorithm. The advantage of using the LMS prior to the genetic algorithm is to optimize the data before giving to the genetic algorithm, thereby limiting the area of the search for an optimal solution. The results show that matched wavelets created using an improved genetic algorithm can detect the HRV variations accurately in the standing and laying postures.

A 30-year-old woman complains of vaginal bleeding in between menstruations.

• Is intermenstrual bleeding normal?
• What are the common causes of intermenstrual bleeding?
• How should her symptoms be investigated?

During the reproductive life-span, almost every woman will experience some changes in the pattern of menstrual flow and menstrual cycle. In the absence of a pregnancy or therapeutic hormonal influence, any uterine bleeding that occurs between otherwise a normal pattern of menstruation is referred to as intermenstrual bleeding.

Two types of IMB can be observed: the bleeding that occurs once only in between otherwise normal menstruations, and those that occurs on and off in between menstruations. The former type of IMB is physiological and occurs in approximately 20–30% of women or 1–2% of all menstrual cycles. Typically, it occurs between day-10 and day-16 of the menstrual cycle and lasts for 12–72 hours. The bleeding is usually scanty or light. It is often described as spotting of blood.

Physiological IMB is associated with ovulation. There is a surge in serum level of estrogen towards the end of the follicular phase. The negative feedback of estrogen to the pituitary gland and the associated surge in luteinizing hormone cause an abrupt dip in the circulating estrogen level just before ovulation. This change in circulating estrogen level precipitates breaking down of endometrium with a resultant uterine bleeding.