The inner lining of the uterus is called the endometrium. The endometrium is the tissue to which a fertilized egg, or blastocycst, attaches for the duration of a pregnancy. The endometrial size varies throughout the menstrual cycle, but should be less than 8 mm in post-menopausal women.
The menstrual cycle lasts approximately one month. During the cycle, a follicle matures and then it ruptures to release an egg that is swept into the fallopian tube for fertilization. The endometrium thickens throughout the menstrual cycle in preparation for egg implantation. If implantation does not occur, the endometrium is expelled, a process called menstruation.
The endometrium starts off as a thickened lining, sometimes measuring up to 15 mm in thickness. Menstruation occurs during the first week of the menstrual cycle. As the endometrium is expelled, it may vary in thickness and may have an irregular appearance on ultrasound. As the week progresses, the endometrium becomes thinner. By then end of menstruation, the endometrium should measure approximately 2 to 3 mm thick.
During the proliferative phase, a follicle begins to grow on one of the ovaries. While this follicle grows, it secretes estradiol, an estrogen that is responsible for the thickening of the endometrium prior to ovulation. Fertility increases during this stage of the cycle. During the proliferative stage, the endometrium can become as much as 8 mm thick. On ultrasound, it has the appearance of three lines.
Ovulation marks the end of the proliferative phase and the beginning of the secretory phase. The mature follicle ruptures and releases an egg, called an ovum. This is called ovulation. Fertility is greatest between five days prior to ovulation and two days after. Some fertility clinics like to see a 1-cm thick endometrium prior to ovulation.
The follicle that ruptured to release the egg is now called the corpus luteum. The corpus luteum releases progesterone. Progesterone is responsible for the further thickening of the endometrium in preparation for blastocycst implantation. During the secretory phase, the endometrium can thicken to as much as 15 mm.
- Ultrasound: The Requisites (Requisites); Alfred B. Kurtz William D. Middleton; 1996
What Are the Causes of an Enlarged Uterus?
Enlarged uterus is a problem common to some women, particularly older women approaching menopause. Many conditions could lead to the enlargement of...
Uterine Cancer Symptoms
Uterine cancer is one of the most common cancers of the female reproductive system. It is also known as sarcoma of the...
What Is the Endometrial Stripe?
The endometrium is the mucous membrane lining of the uterus. It is sometimes referred to as the endometrial stripe because it shows...
Colon Polyps: Cancer
Colon polyps are precursors of colon cancer and are responsible for 90 to 95 percent cases of colon cancer. A colon polyp...
Normal Uterine Thickness After Menopause
Normal uterine thickness changes after menopause. Before menopause, thickness of the uterine lining increases from 1 to 3 mm to 16 mm,...
Fibroid Tumor & Large Blood Clots
Large blood clots from the uterus are often associated with fibroid tumors. The blood clots are often accompanied by heavy cramping and...
Menopause & Thickening of Uterine Walls
Thickening of the uterine walls is a phenomenon experienced by some women during menopause. This condition is benign and, in most cases,...
How to Get Pregnant With Uterine Fibroids
A uterine fibroid is a non-cancerous uterine tumor that grows from muscle walls of the uterus. A uterine fibroid may prevent pregnancy...
What Are the Causes of Thickened Lining in Perimenopause?
Perimenopause is a period of transition between fertility and menopause. This stage can last from 2 to 8 years and includes the...