Menstrual Cycle Overview

Study Notes

Menstruation is the monthly shedding of the uterine lining. It's also known as menses, menstrual period, or menstrual cycle.
The menstrual cycle is the sequence of events preparing the body for pregnancy each month. It begins on the first day of a period and ends on the first day of the following period.
Individual cycles vary slightly, but the process remains the same.

The average cycle length is 28 days. However, a normal cycle can range from 21 to 35 days.

Menses/Menstruation: This phase, beginning the first day of the period, involves the shedding of the uterine lining through the vagina if pregnancy hasn't occurred. Most people bleed for 3-5 days, but 3-7 days is not uncommon.
Follicular Phase: This phase begins on the first day of menstruation and ends with ovulation, an overlap involving follicle-stimulating hormone (FSH) stimulating the ovaries to develop 5-20 follicles (tiny nodules). Usually only one follicle matures into an egg, while the others die.
Ovulation: Typically occurring between days 11-21 of a 28-day cycle, this marks the release of a mature egg into the fallopian tube to travel to the uterus. The egg survives for about 24 hours.
Luteal Phase: If the egg is fertilized progesterone is produced to support early pregnancy. In case of no fertilization, the corpus luteum breaks down and estrogen and progesterone levels drop, returning to the first stage of the cycle.

The ovarian cycle involves the development and release of an egg from the ovaries. This is connected to the hormonal changes of the menstrual cycle.

The uterine cycle focuses on the changes in the lining of the uterus (endometrium) in response to hormonal changes:
- Desquamation (menses): Shedding of the uterine lining.
- Proliferative phase: Thickening of the uterine lining in preparation for a potential pregnancy.
- Secretory phase: Further thickening of the uterine lining, preparing it to receive a fertilized egg.

Most girls start menstruating around age 12. Periods can begin as early as 8 and as late as 16, correlating with the development of breasts and pubic hair.

Common symptoms include mood changes, trouble sleeping, headaches, food cravings, bloating, breast tenderness, and acne.

The typical blood loss during a period is about 60 milliliters (around 2 ounces). A range of 60-80 ml is considered normal.

Bright red: Most likely indicates recent bleeding at the beginning of the cycle.
Dark red: Suggests slightly older blood, a slower flow, and usually it darkens over the cycle.
Pink: Common at the start or end, suggesting light flow.

Periods that happen less than 21 days or longer than 35 days apart, or that haven't occurred for 3 months.
Periods lasting longer than 7 days.
Periods accompanied by severe pain, cramping, nausea, or vomiting.
Bleeding or spotting occurring between periods.

Menstrual cycles are not always perfectly predictable; lengths vary between cycles and ovulation may not occur on the same day every month. This can make cycle prediction challenging.