Many people think of their menstrual cycle as only the few days each month when they have their period. A woman's menstrual cycle actually lasts around 28 days on average but can be between 21 and 35 days, and it consists of four phases: menstruation, follicular, ovulation and luteal. Understanding the different phases of your menstrual cycle can help you track irregularities and give you valuable insight about your reproductive health.
The four phases of your menstrual cycle
Menstrual phase
The menstrual cycle starts with the menstrual phase, which is the shedding of the uterine lining that occurs during your period. The first day of your period is day one of your cycle.
This phase lasts about 3-7 days on average. It is triggered by a drop in estrogen and progesterone levels, which causes the uterus to shed its lining. The average blood loss during a period is around 2-3 tablespoons. Very heavy bleeding or bleeding that lasts longer than seven days may be abnormal and should be evaluated by a healthcare provider. The menstrual phase is also when women experience common period symptoms like cramps, bloating and mood changes.
Follicular phase
After menstrual bleeding stops, the follicular phase begins. During this phase, follicle stimulating hormone (FSH) from the pituitary gland stimulates the ovaries to start maturing follicles. Each of these follicles contain an immature egg. The follicles produce increasing amounts of estrogen, a sex hormone responsible for the regulation of the female reproductive system, to thicken and rebuild the uterine lining in preparation for a fertilized egg. The follicular phase typically occurs between days 10-14.
Ovulation phase
In the middle of the cycle, there is a surge of luteinizing hormone, a hormone that triggers ovulation or the release of a mature egg from the dominant follicle in one of the ovaries. The egg travels down the fallopian tube where it stays for 12-24 hours and can be fertilized by sperm. Ovulation typically occurs on day 14, but it can vary depending on cycle length.
Luteal phase
The luteal phase typically occurs around day 15 to 28. After ovulation, the dominant follicle transforms into the corpus luteum, which is a structure that forms each month and secretes progesterone and some estrogen. Progesterone prepares the uterine lining to become thickened to receive and nourish a fertilized egg. If conception does not occur, the corpus luteum dissolves, hormone levels drop and menstruation begins again.
Why is tracking my cycle important?
Tracking your cycles over time provides insight about what is happening in your body and helps identify if your cycles are regular or irregular. See your healthcare provider if you have no period by age 16, miss three cycles in a row and/or have severe pain, heavy bleeding or other concerns.
For women interested in understanding their reproductive potential, Labcorp OnDemand’s Women's Fertility Ovarian Reserve Test can assess egg quantity. This blood test measures levels of anti-müllerian hormone (AMH), follicle stimulating hormone (FSH) and estradiol. It should be taken on day three of your period to evaluate your ovarian reserve. Knowing your ovarian reserve empowers you to discuss options for fertility and family planning with your healthcare provider.
If you are just getting started with understanding your menstrual cycle, you are not alone. There are resources online and through your healthcare provider that can help you understand your cycle and any irregularities. The first step is knowledge!
