The menstrual cycle is a physiological process that occurs cyclically in all fertile women. The first period of a woman’s life is called menarche, and the last, menopause.

This is a more complete version of the text FERTILE FOR PREGNANT PERIOD . Here we will focus more on the menstrual cycle, explaining in detail the hormonal interactions that lead to ovulation. This text is more conducive to school work and students of biological areas. The other text is aimed at people seeking information about the fertile period. I suggest, in any event, reading either because they are complementary.


The menstrual cycle starts on the first menstruation, lasts about 28 days and ends on the first day of the following menstruation. Some women have shorter periods up to 21 days while others have longer periods, ranging up to 35 days. adolescent women with recent menarche may have cycles of up to 45 days, once your reproductive system is still maturing. The same extension can occur with near-menopausal women, when it begins to be ovarian failure signals.

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The reproductive organs of women consist of two ovaries, two fallopian tubes, a womb and vagina.

female reproductive system

The menstrual cycle is also divided into two phases: the follicular phase and the luteal phase. To facilitate understanding, let us consider the normal cycle that 28 days, 14 days follicular phase and 14 days of luteal phase.

This process is complex and involves the control of various hormones, but I will try to explain it in a very simple way for everyone to understand the basic mechanisms of the menstrual cycle

1) Follicular Phase

The follicular phase begins on the first day of menstruation, i.e., on the first day of the cycle. Earlier this stage, the hormones estrogen and progesterone are low and the uterus is menstruating, apesentando a wall (endometrium) and thin. Ovarian this phase is at rest.

At this time, the pituitary gland (pituitary), which is located in the central nervous system begins to increase production of a hormone called follicle stimulating hormone (FSH) , which as its name implies, stimulates the follicles of the ovary.

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I open here a quick parentheses. Unlike the men who produce their sperm continuously, women are born with a counted number of eggs. There are about 450,000 and they are stored in the ovaries in immature form within the ovarian follicles.

In the presence FSH, follicles begin to develop, grow and mature. Seven days after the start of the cycle, it is possible to detect the ovarian follicles various ultrasound measuring between 9 and 10 millimeters.

These follicles, now begin to produce estrogen. As estrogen levels are growing, one follicle becomes dominant, developing faster than others, which actually stop growing and begin to regress. The dominant follicle grows about 2 mm per day until the final size 20-26 mm, when complete its development. This dominant follicle is who will release the egg at ovulation.

Besides the development of the dominant follicle, estrogen also acts on the uterus, preparing it for a possible pregnancy. The membrane of the uterus wall, endometrium call begins to proliferate, acquiring layers, becoming thus thicker.

2) Luteal Phase

menstrual cycle

ovulatory cycle – Change in hormones

The estrogen peak occurs within 1 day before ovulation. At the time of maximum concentration of estrogen, another hormone from the pituitary gland is released, theluteinizing hormone (LH) . We are now exactly at mid-cycle, 14 day menstrual cycles in cases of 28 days.

The peak of estrogen and rise of LH, make the woman begins to produce a viscous mucus, called fertile mucus, which favors the mobility of sperm.

The release of LH completes the maturation process of the dominant follicle, and approximately 36 hours after its release, the disruption occurs from the follicle and release of the ovum, or a woman ovulates. Click on the image to enlarge the table of the menstrual cycle.

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Some women experience pain at the time of ovulation by peritoneal irritation after the rupture of the ovarian follicle. This pain is located in the lower abdomen, ovary side that ovulated. This pain can last a few hours and usually cyclical, occurring almost tod0 month. This syndrome is called mittelschmerz , which means pain through (cycle) in German.

Shortly after the LH peak that triggers ovulation in women’s body temperature rises slightly, about 0.5 ° C and remained so for 10 days.

Medication temperature is a good method to learn retrospectively if the woman ovulated recently, but this rise usually occurs late in relation to ovulation, not intended to indicate the right time of intercourse.

corpus luteum

Just before ovulation, the cells around the ovarian follicle, under the influence of LH, begin to form the corpus luteum, the structure responsible for producing estrogen and especially progesterone. When the woman ovulates, the egg is released toward the tubes, remaining only the corpus luteum in the ovary.

Throughout the end of the luteal phase, the corpus luteum produces progesterone remains, which acts to inhibit LH secretion by the pituitary. In the uterus, progesterone acts interrupting the proliferation of the endometrium. In fact, progesterone organizes the mucosal layers making it more homogeneous, making it rich in fluids and nutrients to the fetus potential. When you do an ultrasound of the uterus in the proliferative phase of the cycle, it is possible to detect three distinct layers of endometrium. When the same test is done in the luteal phase, there is no such distinction and the endometrium is all uniform, ready to receive the fertilized egg.

Because progesterone inhibits the H, if the egg is not fertilized, the fall of LH causes the corpus luteum begins to involute, which in turn causes the fall in estrogen and progesterone production by the same.Without these hormones the thick wall of the endometrium is no longer tenable, its blood supply is cut off, and it ends up collapsing, featuring menstruation and restarting the cycle in the follicular phase.

Ovulation occurs 14 days before the first day of the next menstruation. So if you menstruated, count 14 days back and know when ovulated.

If the egg is fertilized, the embryo begins to produce a hormone called chorionic gonadotropin, responsible for maintaining the corpus luteum and production of progesterone assets.

Pregnancy tests are based on the dosage of gonadotropin concentrations (read: symptoms of pregnancy | PREGNANCY TEST ).


After his release, the egg is only viable for about 12-24 hours. This means that fertilization is more likely when there are already present sperm before ovulation. Despite the short period of the egg viability, the fertile interval is much longer, because, depending on the quality of the male semen, spermatozoa may be feasible within the woman’s reproductive system for up to 5-7 days. Therefore, the fertile period is from 5 days before ovulation until the day after.

Men with poor quality sperm can have sperm that survive less time, thus reducing the length of the fertile window

The period of greatest chance of fertilization occurs when intercourse one or two days before ovulation.

Current studies have shown that sperm quality is increased when the range is 2 to 3 days between ejaculations. Therefore, it indicates coitus day in , day out, or every 2 days. For couples who want to conceive, a tip is to have sex 3 times a week, starting shortly after the end of menstruation (to learn how to calculate the fertile period, read: CALCULATING THE PERIOD FERTILE ).



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