The number of genera are far fewer; for example, there are a number of species of Polystichum (one of which is the sword fern), and many of them look so similar to the casual observer that it would seem that there are fewer native ferns than is actually the case.
The egg is released around day fourteen in the cycle and the thickened lining of the uterus is to provide nutrients for a potential developing baby. If pregnancy does not occur, the lining is released in what is known as menstruation. A number of problems with menstruation may occur. A lack of periods, known as amenorrhea, is when periods do not occur by age 15 or have not occurred in 90 days. Periods also stop during pregnancy and typically do not resume during the initial months of breastfeeding.
In women with a regular cycle, normal ovary functioning releases one egg about every 25â28 days. Although the average time between periods varies depending on the woman, especially during puberty and the perimenopause periods, most women will have their periods once monthly when theyâre in good health.