The menstrual cycle consists of several stages, or phases, that the female body needs to go through to prepare for the possibility of becoming pregnant each month. Hormone fluctuations are responsible for transitioning the body from one phase to the next.
There are four phases of the menstrual cycle. These are:
- the menstrual phase
- the follicular phase
- the ovulation phase
- the luteal phase
The length of each phase can vary from person to person. The length of each phase can also change over time and with age.
Keep reading for more information on each of these four stages of the menstrual cycle.
The menstrual phase is the first phase of the menstrual cycle. This is the part of the cycle when a person has their period.
Because the thickened uterine lining is not needed, it will break down and shed. This lining and the egg then exit through the vagina during the menstrual period.
The period consists of a combination of uterus tissue, mucus, and blood. The menstrual phase can last for 3–8 days.
During this phase, a person may experience:
The follicular phase, which some people call the proliferative phase, also starts on the first day of a person's period. It is simultaneous with the menstrual phase.
At the start of the cycle, a brain region called the hypothalamus signals the pituitary gland to release follicle stimulating hormone (FSH).
FSH stimulates the ovaries to create several small sacs called follicles. These each contain an immature egg. The healthiest egg will mature while the rest of the follicles will absorb back into the body.
As the follicle matures, the body releases extra estrogen. This stimulates the uterine lining to thicken. The thickened lining can provide the necessary nutrients to a fertilized egg.
The follicular phase typically lasts around 10–16 days. This phase will end when a person ovulates.
The ovulation phase starts when rising estrogen levels signal the pituitary gland to release luteinizing hormone (LH). LH stimulates the process of the ovary releasing a mature egg. This process is called ovulation.
During ovulation, the mature egg travels from the ovary, down the fallopian tube, and into the uterus. At any time during the egg's journey, sperm can fertilize it.
People who wish to conceive can watch for signs such as thick, white discharge from the vagina and a slight increase in their basal body temperature. A person can measure their basal temperature at home using a sensitive thermometer.
Ovulation typically occurs in the middle of the menstrual cycle. The egg can survive for about 24 hours before it needs to be fertilized. If it does not become fertilized during that time, the egg will dissolve.
The final phase of the menstrual cycle is called the luteal phase.
During the luteal phase, the follicle morphs into a mass of cells called the corpus luteum. The corpus luteum releases progesterone, which will keep the uterine wall thick and ready for a fertilized egg to implant.
If the egg becomes fertilized, the body will produce human chorionic gonadotropin (hCG). hCG helps keep the uterine lining thick for the fertilized egg to develop into an embryo.
However, if the egg does not become fertilized during ovulation, the corpus luteum will dissolve into the body. Both estrogen and progesterone levels will drop, which marks the beginning of the menstrual phase.
During the luteal phase, a person may experience symptoms of premenstrual syndrome (PMS). These may include:
- mood changes
- pain, tenderness, or swelling of the breasts
- changes in sex drive
- weight gain
- difficulty sleeping
- food cravings
The length of the luteal phase can vary, but it tends to be around 14 days on average.
People's experiences of the menstrual cycle can vary greatly. Differences can include the length of the cycle, the heaviness of the period, and the severity of any PMS symptoms.
A person's menstrual cycle can also change at different points during their life, such as before menopause.
Sometimes, it can be difficult to identify issues with the menstrual cycle. A person can track their periods by recording when they start and stop. This will help improve their awareness of any problems or changes.
It may also be helpful to record the heaviness of the bleeding and whether or not any spotting occurs.
Certain events and conditions can affect a person's menstrual cycle. These can include:
If a person notices any changes to their menstrual cycle, they should talk to a doctor. They may be able to help diagnose and treat any underlying issues.
Some symptoms to watch for and discuss with a doctor include:
- irregular periods
- absent or skipped periods
- bleeding between periods
- bleeding that lasts for longer than 7 days
If a person experiences these or any other noticeable issues, they should speak to a doctor as soon as possible.