The endometrium is the inner lining of the uterus, a dynamic tissue that changes monthly in preparation for potential pregnancy. It provides a receptive environment for a fertilized egg. If pregnancy doesn’t occur, this lining sheds during menstruation. Its thickness indicates uterine health and fluctuates with hormones, making understanding typical thickness important for reproductive well-being.
Normal Endometrial Thickness
Endometrial thickness varies considerably throughout life and the menstrual cycle, driven by estrogen and progesterone. During menstruation, it is thinnest (1-4 mm) as shedding occurs.
In the early proliferative phase (days 5-14), estrogen causes the lining to gradually thicken to 5-8 mm, reaching 10-16 mm by the late proliferative phase. Around ovulation, it often measures 7-14 mm. In the secretory (luteal) phase, progesterone helps maintain and further develop the lining for possible embryo implantation, typically ranging from 7-18 mm.
For post-menopausal individuals not using hormone replacement therapy (HRT), the endometrium is generally 5 mm or less due to decreased estrogen. However, for those on HRT, the lining may be thicker, sometimes up to 15 mm.
Understanding Thin Endometrium
A thin endometrium refers to a uterine lining thinner than expected for the menstrual cycle phase or reproductive state, often defined as less than 7 mm. Low estrogen levels are a common cause. Hormonal imbalances, including those from polycystic ovary syndrome (PCOS), can disrupt the normal thickening process.
Certain medications, such as clomiphene citrate (used for ovulation induction) or long-term oral contraceptive use, may also contribute. Prior uterine procedures, like dilation and curettage (D&C), or conditions such as Asherman’s syndrome (intrauterine adhesions), can damage the lining and lead to scarring. Poor blood flow to the uterus, influenced by smoking, obesity, or high blood pressure, can also impede growth.
While sometimes asymptomatic, indicators include irregular or light menstrual periods. A thin endometrium can impact fertility, hindering embryo implantation and increasing miscarriage risk.
Understanding Thick Endometrium
A thick endometrium occurs when the uterine lining grows beyond expected thickness for a particular stage. This is frequently linked to hormonal imbalances, especially excess estrogen without sufficient progesterone to regulate its growth. When progesterone is not adequately produced, the lining continues to grow rather than shedding, leading to thickening. Endometrial hyperplasia, a benign overgrowth of endometrial cells, is a common result.
Other factors include uterine polyps (growths from the inner lining) and fibroids (benign muscle growths in the uterine wall). Medications like tamoxifen, used in breast cancer treatment, can also stimulate thickening.
Symptoms often include abnormal uterine bleeding, such as heavy or prolonged periods, bleeding between periods, or any bleeding after menopause. While many causes are benign, some hyperplasia types, particularly atypical hyperplasia, carry an increased risk of progression to endometrial cancer.
Diagnosis and Clinical Approach
Endometrial thickness is primarily measured using transvaginal ultrasound, a non-invasive imaging technique that provides detailed views of the uterus. If abnormal thickness is detected, further investigation is often recommended to determine the underlying cause.
This may include saline infusion sonography (SIS), where saline is gently introduced to enhance ultrasound visualization. An endometrial biopsy, involving removal of a small tissue sample for microscopic examination, is a common next step to check for abnormal cells. Hysteroscopy, where a thin, lighted tube is inserted to visually inspect the uterus, can also be performed.
Management strategies depend on the specific diagnosis, symptoms, age, and reproductive goals. Approaches can range from watchful waiting and hormonal therapy to surgical interventions like polypectomy, dilation and curettage (D&C), or hysterectomy. Consulting a healthcare professional is important for accurate diagnosis and personalized treatment recommendations.