Menstrual cycle

The process of ovulation and menstruation regulated by hormones so as to prepare the female body for pregnancy is known as menstrual cycle. Menstrual cycle is essentially divided into the following phases:

  • Follicular phase inclusive of menstrual phase
  • Ovulation phase
  • Luteal phase

Menstrual phase (Day 1 to Day 5)

First full day of bleeding is referred to as the Day 1 of the cycle. The menstrual phase begins from day 1 of the bleeding and lasts till the 5th day of the cycle. During this phase, following events take place:

  • The uterus sheds its innermost lining consisting of soft tissues and blood, which is expelled from the vagina in the form of menstrual fluid loss.
  • Uterine and abdominal muscles contract to enable expulsion of the menstrual fluid and abdominal cramping sensation is experienced.

Follicular phase (Day 1 to Day 13)

Follicular phase also begins on day 1 of the menstruation and lasts till about the 13th day of the cycle. During this phase, following events take place:

  • The levels of estrogen and progesterone hormones that had dropped at the end of the previous cycle send a signal to pituitary gland in order to increase the production of FSH (follicular stimulating hormone).
  • This surge in FSH stimulates the egg containing follicles in ovaries to grow.
  • This causes FSH to go down till the time only one of these eggs is left to mature in a sac which is referred to as dominant follicle.
  • It takes about 13 days for the egg to reach its maturity.
  • This dominant follicle releases estrogen, which increases the thickness of uterine lining, so as to prepare for pregnancy, and also, thins cervical mucus to enhance the movement of the sperm.

Ovulation Phase

With the increased estrogen production from dominant follicle, the pituitary gland secretes the Luteinizing Hormone or LH. This LH surge helps dominant follicle mature and release the egg contained inside. The change that happened to the cervical mucus during the follicular phase allows the sperm to pass through the cervix and uterus to the fallopian tube. The sperm can survive in this environment for about 72 hours while waiting for the egg to arrive, but the egg, on the contrary, can only survive for about 24 hours before it must be fertilized by a single sperm. Once fertilization takes place, a membrane surrounds the egg which hardens up to form a shell so that another sperm cannot enter. The genetic material now combines and starts multiplying to become an embryo which then travels back to uterus for implantation.

Post Ovulation Phase

The empty follicle from which egg has already been released secretes progesterone. This progesterone helps enable uterine lining to provide nourishment as well as implantation site for the embryo in the uterus. The embryo travels back to the uterus and in about four days of fertilization, implants itself in the uterus. This embryo now starts to produce pregnancy hormone HCG (Human Chorionic Gonadotropin) which is measured in pregnancy tests for confirmation of the same. This hormone’s presence stimulates ovaries to make estrogen and progesterone so as to support pregnancy. In case, the fertilization does not take place, absence of the same HCG hormone, triggers ovaries to stop the production of estrogen and progesterone. When these hormonal levels come down, the uterine lining sheds causing the next menstrual period to begin.

Abnormalities related to menstrual cycle

  • Dysmenorrhea – This is a condition, which refers to painful severe cramping accompanying menstrual periods. Sometimes Dysmenorrhea is related to some underlying complications like uterine fibroids or endometriosis.
  • Primary Amenorrhea – When a female has turned 16 but has not started to menstruate, the condition is referred to as primary amenorrhea.
  • Secondary Amenorrhea – If a female has regular periods, but all of a sudden the periods stop, the condition is referred to as secondary amenorrhea.
  • Heavy Menstrual Bleeding – Some women have prolonged menstrual periods and bleeding, which is more than normal to the extent that they have difficulty carrying on with their day-to-day lives.
  • Oligomenorrhea – Light or infrequent menstruation where menstrual periods are set more than 35 days apart or the flow of periods is very light.
  • Premenstrual Syndrome – Range of physical as well as psychological symptoms that are associated with menstrual cycles are referred to as premenstrual syndrome. Sometimes symptoms can be quite severe including bloated feeling, headaches, fatigue, constipation, or painful breasts. Some women also experience mood swings, anxiety or depression, because of which, they sometimes find it difficult to manage.

When Do I Ovulate?

Typically, ovulation occurs almost halfway through the cycle. An average cycle is believed to last about 28 days counting from day one of bleeding to the first day of the next period. To find out the time of ovulation, one can subtract 14 days from the number of days in the cycle. The cycle is the number of days from the starting of a period to the start of next period. So, for an average cycle (believed to be 28 days), ovulation can be expected on day 14.

Most Fertile Time of the Cycle

Fertile window is considered the best time of the cycle for conception. This fertile window can be different for each woman and is mostly dependent on the length of menstrual cycle. Technically speaking, pregnancy is only possible during the five days leading to ovulation and on the day of ovulation as the lifespan of ovum is only 24 hours and that of sperm is about 5 days.  If a female has intercourse before six days of ovulation, the chances of pregnancy are almost nil, but if she has intercourse during the five-day window of ovulation, the chances are that sperm is able to thrive and meet the ovum as soon as ovulation happens; thus, leading to pregnancy.  The probability of becoming pregnant in this fertile window is dramatically high, especially if intercourse happens in three days leading to and including the day of ovulation.

Irregular Cycles and Their Effect on Your Fertility

Since three days leading up to and including ovulation are considered to be most fertile, the most fertile days in the cycle vary, depending on your cycle length:

  • If a female has 28 days between two menstrual cycles, ovulation typically happens on day 14, and the most fertile days are believed to be days 12, 13, and 14.
  • If a female has longer cycles, say about 35 days between two menstrual cycles, ovulation happens on day 21 and the most fertile days are days 19, 20, and 21.
  • If a female has shorter cycles, say about 21 days between periods, ovulation happens on day 7 and the most fertile days are days 5, 6, and 7.

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