With the lower dose of estrogen, it is more likely that ovulation is not always suppressed or disrupted and the cervical and endometrial factors become significant. In those circumstances, the endometrial and cervical factors are essential for the prevention of the development of pregnancy. A constant level of progestogen would be needed to main the cervical factor. The cervical mucus and endometrial effects of the progestogen, although a back-up in case ovulation suppression fails, are thus probably no so significant in those formulations. Tricyclic Pills Athletes competing at sporting events, women marrying and wanting the wedding night free of menstruation, women undergoing academic examination and women simply not wanting the inconvenience of monthly cycles may choose to extend the twenty-one days of pill taking.
Tricyclic pills extend the menstrual cycle to three months.
The combined pill mainly suppresses ovulation and also has the back-up effects on the endometrium and the cervix. The woman experiences something like menstruation only after she stops taking the pill. The manufacturers choose to do it that way, mimicking the normal menstrual cycle.