Menstrual Cycle

The menstrual cycle is a regular, natural change in the female reproductive system that makes pregnancy possible. Females of reproductive age go through cycles of hormonal changes roughly every month, preparing the body for potential pregnancy. If pregnancy does not occur, the body sheds the uterine lining, a process called menstruation.

Phases of the Menstrual Cycle

A typical menstrual cycle lasts around 28 days, although it can vary. The cycle has three main phases:

1. Follicular Phase: The cycle starts with the follicular phase, where the body prepares an egg for ovulation. This phase involves increased estrogen levels and the development of ovarian follicles.
2. Ovulatory Phase (Ovulation): Around mid-cycle, luteinizing hormone (LH) surges, triggering ovulation. The dominant follicle releases an egg into the fallopian tube, where it remains viable for up to 24 hours.
3. Luteal Phase: After ovulation, the remaining follicle forms a structure called the corpus luteum, which releases progesterone. This hormone prepares the uterine lining for potential implantation. If implantation does not occur, hormone levels drop, and the menstrual cycle starts again with menstruation.

Hormones Involved in the Menstrual Cycle

Four main hormones regulate the menstrual cycle:

• Follicle-Stimulating Hormone (FSH): Stimulates follicle development in the ovaries.
• Luteinizing Hormone (LH): Triggers ovulation.
• Estrogen: Thickens the uterine lining and regulates other cycle phases.
• Progesterone: Prepares the uterus for potential embryo implantation after ovulation.

Symptoms and Menstrual Disorders

Many women experience symptoms one to two weeks before menstruation, commonly known as premenstrual syndrome (PMS). Symptoms can include acne, tender breasts, bloating, fatigue, irritability, and mood changes. For about 20–30% of women, these symptoms interfere with daily life, while 3–8% experience severe symptoms.

Menarche, Cycle Length, and Menopause

• First Menstrual Period (Menarche): Typically occurs between ages 12 and 15, although it can happen earlier or later.
• Cycle Length: In young women, cycles range from 21 to 45 days, while adults generally have cycles lasting 21 to 31 days.
• Menopause: Menstruation stops between ages 45 and 55, marking the end of reproductive years.

Menstrual Cycle Control with Hormonal Contraception

Hormonal contraceptives can alter the menstrual cycle to prevent pregnancy. By regulating hormone levels, these methods control ovulation and the cycle itself.

Summary of Menstrual Cycle Phases

The menstrual cycle can also be described by events in the ovary and uterus:

• Ovarian Cycle Phases: Follicular phase, ovulation, and luteal phase.
• Uterine Cycle Phases: Menstrual phase (shedding), proliferative phase (thickening), and secretory phase (preparation for implantation).