The female body is an amazing thing! Each month, from millions of tiny follicles, we produce one mature egg ready for release at ovulation. This egg carries genetic material perfectly designed to match with the genetic material in sperm. This perfect fusion then has the ability to conceive and grow into another human being.
For this amazing cycle of events to take place, and conception and pregnancy to occur, we need the menstrual cycle. Commonly referred to as your period, rags or ‘that time of the month’, the primary role of the menstrual cycle is to not only release the egg at ovulation, but to help ensure a healthy environment to help facilitate a healthy conception and pregnancy. The menstrual cycle helps keep the uterine conditions ideal for conception and implantation by regularly shedding the uterine lining (endometrium) each month.
An average menstrual cycle lasts 28 days, with ovulation occurring on day 14. However, in reality only around 20 percent of women have an ‘average’ cycle with most menstrual cycles lasting anywhere between 21 and 35 days.
The menstrual cycle is regulated by two major hormones – follicle stimulating hormone (FSH) and luteinising hormone (LH). The balance of these hormones stimulates ovulation and promotes the production of either progesterone or estrogen in the ovaries.
There are three major phases of the menstrual cycle
- Phase 1 – Follicular Phase
- Phase 2 – Ovulatory Phase
- Phase 3 – Luteal Phase
The Follicular Phase
This phase commences on the first day of the menstrual bleed. Both estrogen and progesterone levels are low at this point. This drop in both hormones facilitates the shedding of the uterine lining (endometrium) to form the menstrual bleed.
Menstrual bleeding typically lasts around 3 – 5 days but can vary anywhere from 2 – 7 days. Anything shorter on longer may indicate that there’s an underlying issue that needs addressing and it’s advised to seek advice from your health care professional. During these 2 – 7 days FSH begins to rise. This rise in FSH, stimulates growth within the follicles. This growth continues during the follicular phase, culminating in the development of one dominant follicle, housing one mature egg (or in rarer cases 2 or more eggs – multiple birth) ready to be released at ovulation. As the follicles develop they produce increasing amounts of estrogen. This increase in estrogen levels stimulates the thickening of the uterine lining (endometrium) in preparation for potential implantation of a fertilised egg after ovulation.
Estrogen continues to rise during this phase, reaching a peak just before ovulation. FSH also continues to rise but then drops slightly before ovulation. The average follicular phase lasts around 13 – 14 days with ovulation occurring on day 13 or 14. However this phase is the most likely to vary significantly in length, which also varies the timing of ovulation.
The Ovulatory Phase
The peak in estrogen just before ovulation, triggers a surge in LH. This LH surge triggers the rupture of the dominant follicle releasing the mature egg (or in rarer cases multiple eggs) in a process we know as ovulation. FSH also rises slightly at ovulation then both LH and FSH levels sharply decline once ovulation has occurred and the egg has been released.
After ovulation, the egg then makes it’s way down the fallopian tubes towards the uterus. It is during this journey that the egg can be fertilised by sperm and the process of conception and pregnancy commences.
If fertilisation doesn’t occur, the egg will degenerate in the uterus about 12 – 24 hours after its release from the ovary at ovulation and will then be shed during the next menstrual bleed. The average ovulatory phase lasts around 16 – 32 hours, beginning with the surge in LH and ending when the egg is released at ovulation.
For some women, ovulation may come and go with few if any signs or symptoms. Others may experience ovulation signs such as slight cramping on pain, generally on one side, breast tenderness, bloating, heightened sex drive or light spotting. There are also other, less obvious, ovulation signs occurring in your cervical fluid and position as well as your body temperature. These ovulation signs can be measured to help ascertain when ovulation is occurring. Measuring these ovulation signs each month and being aware of when ovulation is occurring increases your chances of conceiving each month. (Learn how to track your ovulation signs)
The Luteal Phase
During the luteal phase, the follicle that ruptured to release the egg at ovulation, closes and forms the corpus luteum. The corpus luteum then releases increasing levels of progesterone, which becomes the dominant hormone during this phase. Progesterone helps prepare the uterine lining (endometrium) for potential conception and implantation of a fertilised egg. If conception doesn’t occur and an egg is not fertilised, the corpus luteum will regress about 14 days after it’s formed. This regression will signal a drop in both estrogen and progesterone, which will stimulate the shedding of the uterine lining (endometrium) and the beginning of a new menstrual cycle.
If conception does occur and an egg is fertilised and implanted into the thickened uterine lining (endometrium), the cells around the fertilised egg will secrete human chorionic gonadotropin hormone. This hormone will maintain the activity of the corpus luteum, which, instead of regressing, will continue to release progesterone until the foetus develops enough to be able to take over its own hormone production. It is this hormone that pregnancy tests detect to indicate that conception has occurred and you are pregnant! Of course in this case, the menstrual cycle will not recommence, instead this will signal the beginning of a pregnancy.