What is the follicular phase of the menstrual cycle. How long does it last?

The follicular or pre-ovulatory phase of the menstrual cycle is the period between the first day of menstruation and ovulation. Therefore, in a typical 28-day menstrual cycle it lasts 14 days, although its length is more variable than that of the luteal or postovulatory phase.
The follicular phase, also called the proliferative or pre-ovulatory phase, is the stage of a woman's menstrual cycle when the ovarian follicles grow. This stage comprises from the onset of menstruation, that is, from the first day of menstruation until the ovulatory phase. Estrogen and progesterone levels at the beginning of the follicular phase of the menstrual cycle are low so that the endometrium can be shed and cause menstruation. In addition, follicle stimulating hormone (FSH) increases in concentration so that follicular development can occur. As this occurs and the follicles are developing, the ovaries begin to secrete estrogen.
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