The endometrium is a specialized tissue lining the inside of the uterus. Its thickness indicates uterine health and function.
The Endometrium’s Purpose
The endometrium is crucial for reproduction. Each month, hormones like estrogen and progesterone cause it to grow and thicken. This prepares a hospitable environment within the uterus for a fertilized egg. If conception occurs, the endometrium supports the embryo’s early development. If not, its functional layer sheds, resulting in menstruation.
Typical Thickness Through Life Stages
Endometrial thickness varies throughout a person’s life and menstrual cycle phases. During menstruation, the lining is thinnest, measuring 1 to 4 millimeters (mm). In the early proliferative phase, it rebuilds to 5 to 7 mm. As the cycle progresses into the late proliferative phase, thickness reaches approximately 11 mm.
Following ovulation, in the secretory or luteal phase, it reaches maximum thickness, ranging from 7 to 16 mm, sometimes up to 18 mm. For postmenopausal women not on hormone replacement therapy, the endometrium is thinner, usually 3 to 5 mm or less. For those on hormone replacement therapy, thickness can be greater, up to 15 mm, with 8 to 11 mm often acceptable.
When Thickness Deviates from Normal
Deviations from these typical thickness ranges can indicate various underlying health conditions. An abnormally thin endometrium is generally less than 7 mm. A thin lining can hinder successful implantation and increase miscarriage risk.
Several factors can contribute to a thin endometrium. These include hormonal imbalances, particularly low estrogen. Other causes are reduced uterine blood flow, scarring from previous surgeries or infections (e.g., Asherman’s Syndrome), chronic inflammation, or certain medications. Polycystic Ovary Syndrome (PCOS) can also lead to thinner endometrial tissue due to hormonal disruptions.
Conversely, an abnormally thick endometrium is also a concern. When the lining exceeds the expected measurements for a given cycle phase or menopausal status, it may signal an underlying issue. A common cause is hormonal imbalance, specifically excess estrogen not balanced by progesterone. This can lead to endometrial hyperplasia, where the uterine lining becomes excessively thick. Atypical hyperplasia carries an elevated risk of progression to endometrial cancer.
Other reasons for a thickened endometrium include endometrial polyps (usually benign tissue growths) or uterine fibroids (benign muscle growths within the uterus). In postmenopausal women, thickness exceeding 5 mm often warrants further investigation.
Assessing and Addressing Endometrial Thickness
Healthcare providers assess endometrial thickness using diagnostic methods. Transvaginal ultrasound is the most common tool. This procedure involves inserting a small probe into the vagina, which uses sound waves to create images of the uterus and measure the endometrial thickness.
If ultrasound findings suggest abnormal thickness, further diagnostic procedures may be recommended. These include hysteroscopy, where a thin, lighted scope visualizes the inside of the uterus. An endometrial biopsy may also be performed, removing tissue samples for microscopic examination to identify abnormal cells or conditions like hyperplasia or cancer. In some cases, a dilation and curettage (D&C) procedure might be performed to remove tissue. Management of abnormal endometrial thickness depends on the underlying cause identified through these assessments.