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Understanding the Normal Menstrual Cycle

The menstrual cycle is a complex hormonal process. It results in the development and release of a mature oocyte (egg). If the oocyte is fertilized, it can result in pregnancy. If not, it results in a menstrual period. The menstrual cycle is controlled by hormones released from the pituitary gland in the brain, the ovaries, and the uterus. This complex relationship of the pituitary gland, the ovaries, and the uterus is responsible for the production of the hormones needed for the development of the woman’s oocyte (egg) each month. It also controls the preparation of the womb to support pregnancy should fertilization occur. And it controls the shedding of the thickened uterine lining (menstruation) if no fertilization of the egg occurs. Below is a basic description of the menstrual cycle.

Front view of uterus, fallopian tubes, and ovaries. Half has been cross sectioned to show inside. Vagina is opening to outside. Cervix is lower part of uterus connected to vagina. Two fallopian tubes lead from uterus to ovaries, one on either side of uterus. Ovaries have developing eggs inside. Uterus is lined on inside with endometrium.

An Oocyte (Egg) Develops and is Released

When a woman reaches puberty, the monthly menstrual cycle will begin. Each month, hormonal changes (rising levels of Estrogen, FSH, and LH) cause one or more follicles (undeveloped eggs) to develop and grow. Generally only one follicle becomes dominant. Ovulation [release of mature oocyte (egg)] occurs about day 14 of the normal 28-day cycle. This first part of the cycle is called the “follicular phase.” It is under the control of the Follicle Stimulating Hormone (FSH).

The Oocyte Travels from the Ovary to the Fallopian Tube

Oocytes (eggs) are female reproductive cells stored in the ovaries. During each cycle, one oocyte matures and is released from an ovary. This is called ovulation. The oocyte then travels from the ovary to a fallopian tube. It is guided by the fingerlike projections called fimbria that project over the ovaries on both sides. Progesterone released from the ovary after ovulation causes the uterine lining to thicken. If sperm are present in the opening of the fallopian tube or in the tube itself, the egg may be fertilized. This results in pregnancy. 

If the Oocyte Is Not Fertilized

If pregnancy doesn’t occur, the thickened lining of the uterus is no longer needed. After about 14 days, hormone levels decline. The lining of the uterus then disintegrates and is shed through the vagina. This results in a menstrual period.

How Long Is Each Cycle?

It is normal for a cycle to take 20 to 36 days. For teenagers, the time between periods might be more or less. For adults, it will be around a month from the first day of one period to the first day of the next. That’s why you may hear women talk about a “monthly cycle.”

How Long Does a Period Last?

It’s normal for a period to last 2 to 8 days. Talk to your health care provider if your period lasts longer than 8 days for 2 cycles in a row.

When Can I Become Pregnant?

Generally, fertilization of the egg by the sperm occurs at the time of ovulation. This is usually around day 14 of the menstrual cycle. Rarely, this can happen during the menses (period). Sperm can also survive after intercourse for several days inside a woman’s body. Discuss contraceptive methods and safe sexual practices with your health care provider. This will help you avoid any unintended pregnancy or a sexually transmitted infection (STI).

Author: StayWell Custom Communications
Last Annual Review Date: 9/25/2014
Copyright © The StayWell Company, LLC. except where otherwise noted.
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