Ovulation is one of the many phases of the menstrual cycle. The menstrual cycle is the body’s way of preparing for a possible pregnancy by growing a thickened lining in the uterus that can hold a fertilized egg. If there is no fertilized egg, the body will shed the lining, which causes menstrual bleeding.
How Long Is the Average Menstrual Cycle
The cycle is measured from day one when menstruation begins, until day one when it begins again. The average duration of a monthly cycle is 28 days, but many women experience cycles that are longer or shorter.
The menstrual cycle passes through three phases: menstruation, the follicular phase, and the luteal phase. Each phase is triggered by hormonal changes.
How Long Is the Follicular Phase?
The follicular phase is defined as beginning with the commencement of menstruation up to, but not including, the spike in LH.
During the follicular phase, hormones in the body stimulate the growth of the follicles in the ovaries, which house the eggs and lasts until one egg is mature enough to be released.
During menstruation, the estrogen levels in the body are low, which triggers the pituitary gland to begin producing follicle-stimulating hormone (FHS). FHS stimulates the ovaries to mature an egg within the ovaries’ follicles. By about day seven, this follicle growth stimulates the production of estrogen, which signals the endometrium (lining of the uterus) to begin thickening again. These high estrogen levels suppress the pituitary gland’s production of FHS, which in turn stops any further eggs from maturing. The follicular phase lasts thirteen days on average.
A study published in the British Journal of Obstetrics and Gynaecology found that a woman’s age seems to be related to how long the follicular phase lasts. The study found that there was a significant decrease in follicular phase length with age–women aged 18-24 years averaged 14.2 days, while women 40-44 years averaged 10.4 days.
How Long Is the Luteal Phase?
The luteal phase is defined as the first day of the LH spike until the commencement of menstruation.
The luteal phase is the phase in which the body ovulates. During the luteal phase, the hormones signal the release of the egg that matured during the follicular phase, and sends it on its journey through the fallopian tubes.
The luteal phase begins around day 13 when the high estrogen levels signal the production of gonadotropin-releasing hormone (GnRH), which will signal the release of luteinizing hormone (LH). The spike in LH signals the beginning of ovulation. The spike in LH causes the follicle encompassing the egg to rupture and it begins its decent through the fallopian tubes. The empty follicle begins secreting estrogen and progesterone, which in turn suppress the levels of FSH and LH.
Soon after ovulation, the empty follicle stops secreting the estrogen and progesterone, which were responsible for maintaining the thickened lining. Unable to sustain itself, the lining is shed and menstruation begins. The luteal phase generally lasts for 12-14 days.
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Relationship between menstrual cycle phases and cognitive function in females who use and do not use oral contraceptives
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Lenton EA; British Journal of Obstetrics and Gynaecology
Normal variation in the length of the follicular phase of the menstrual cycle: effect of chronological age
1984; Volume: 91; No: 7; pp: 681-4
Luteal Phase Defect