What is the normal thickness of the endometrium?

The normal thickness of the endometrium varies significantly depending on the phase of the menstrual cycle and the patient’s reproductive status. In premenopausal women, endometrial thickness typically ranges from approximately 2–4 mm in the early follicular phase (just after menstruation), increases to 8–14 mm during the late proliferative and secretory phases (just before menstruation), and may reach up to 16 mm in some healthy individuals near ovulation or in the mid-luteal phase. During menstruation, the functional layer sheds, resulting in a thin, often indistinct endometrium.

In postmenopausal women not receiving hormone therapy, an endometrial thickness ≤ 4 mm is generally considered normal and reassuring for endometrial pathology. An endometrial thickness > 4–5 mm in this population warrants further evaluation—especially if accompanied by vaginal bleeding—as it may indicate endometrial hyperplasia, polyps, or malignancy. However, asymptomatic postmenopausal women with a thin endometrium (< 4 mm) have a very low risk of endometrial cancer.

It is important to interpret endometrial thickness in clinical context: imaging modality (transvaginal ultrasound is standard), patient symptoms (e.g., abnormal uterine bleeding), hormonal status, and use of exogenous hormones (e.g., unopposed estrogen or tamoxifen). Thickness alone is not diagnostic; histopathologic evaluation via endometrial biopsy or hysteroscopy remains the gold standard when pathology is suspected.