What are the causes of thickened lining in perimenopause?

Updated February 21, 2017

Perimenopause is a period of transition between fertility and menopause. This stage can last from 2 to 8 years and includes the year following a woman's final menstrual period. Women typically experience perimenopause after the age of 40, but some reach this stage in their mid-30s. One of the most notable changes associated with perimenopause is the reduction and irregularity of menstrual bleeding due to the thickening of the uterus lining (endometrium). This thickening is due to several biological processes.

Hormonal Fluctuations

During perimenopause, the body's normal production of oestrogen and progesterone fluctuates. These hormones cause the uterine lining to thicken so that the body's nutrients can nourish a fertilised egg. Since women may still ovulate during perimenopause, the lining will continue to thicken with increased hormone production, especially in women who are continuing hormonal birth control.

Irregular Periods

Women experience increasing irregularity in the menstrual cycle due to hormonal fluctuations. When periods or spotting occur frequently, the uterine lining remains thin, and periods are typically light. After a long period without menstrual bleeding, however, the uterine lining continues to thicken. This extended build-up results in abnormally heavy or long-lasting periods.

Uterine Lining Abnormalities

Fibroids are noncancerous growths that can build up in or around the uterus and can cause unusually heavy bleeding. These dense, fibrous tissues are nourished by blood cells and can range in size from microscopic growths to as large as a 5-month foetus. Submucosal uterine fibroids grow along the endometrium and protrude inward, thickening the uterine lining as a result. Though the exact cause of fibroid development is unknown, most health care professionals believe they are stimulated by oestrogen surges, which frequently occur during perimenopause or hormone therapy treatments.

Other abnormalities include the development of polyps, also called hyperplasia, which is simply an overgrowth of the uterine lining.


Though the chances of conception are drastically reduced during perimenopause, women may still get pregnant during ovulation in this transition period. Thickening of the endometrium may occur due to pregnancy; vaginal bleeding can thus occur normally, as a sign of potential miscarriage or as a result of an ectopic pregnancy (a fertilised egg that has not exited the Fallopian tube).

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About the Author

Laura Crawford-Adiletta became the in-house copy editor of "Cleveland" magazine in 2008, where she also worked as a section and special project editor. Crawford-Adiletta's work won an award from the Ohio Society of Professional Journalism in 2009. She earned her Bachelor of Arts in English from Case Western Reserve University.