What is the normal thickness of the endometrium lining in a female patient of reproductive age with no known medical history or risk factors?

Normal Endometrial Thickness in Reproductive Age Women

In reproductive age women with regular menstrual cycles, normal endometrial thickness varies throughout the cycle, ranging from approximately 5-6 mm in the early follicular phase to a maximum of approximately 12 mm at ovulation, with a characteristic triple-layer appearance developing in the late follicular phase. 1

Endometrial Thickness by Menstrual Cycle Phase

Early to Mid-Follicular Phase (Days 1-7 after menstruation)

• The endometrium appears as a single thin echogenic line on transvaginal ultrasound from menstruation through approximately day -7 (7 days before ovulation) 1
• Thickness ranges from approximately 5-6 mm during this phase 1

Late Follicular Phase (Days -6 to -1 before ovulation)

• A characteristic change from one to three thin echogenic lines develops, with increasing hypoechogenic (darker) texture between the lines 1
• This triple-layer appearance corresponds to rising estradiol levels and increasing endometrial thickness 1
• The endometrium progressively thickens during this phase in response to estrogen stimulation 1

Periovulatory Period (Day of ovulation)

• Maximum hypoechogenic texture is observed between the three echogenic lines, which become thicker at ovulation 1
• Mean endometrial thickness at ovulation is approximately 12 mm (measuring both layers combined) 1
• This represents the peak thickness in the normal menstrual cycle 1

Luteal Phase (Days +1 to menstruation)

• From days +1 to +6 after ovulation, progressive blurring of the three lines occurs with the previously hypoechogenic layers displaying more echogenic (brighter) texture 1
• From day +7 through menstruation, the three lines become indistinguishable due to general hyperechogenic texture of the endometrium 1
• Endometrial growth plateaus during the luteal phase with no further significant thickening 1

Clinical Significance and Measurement Technique

• Endometrial thickness should be measured as a double-layer measurement (both anterior and posterior layers combined) on transvaginal ultrasound 2
• The normal cyclical changes in endometrial texture and thickness are important tools for evaluating normal ovulatory endometrial development 1
• These measurements are particularly useful in monitoring stimulated cycles in assisted reproduction treatment modalities 1

Important Caveats

• Endometrial thickness measurement has limited diagnostic value in premenopausal women and should not be used to exclude pathology 3
• Clinical symptoms, particularly abnormal uterine bleeding, rather than thickness measurements alone, should guide decisions for endometrial sampling in reproductive age women 3
• Even with endometrial thickness <5 mm in premenopausal women, endometrial polyps or other pathology may still be present 3
• The appearance on MRI shows that normal endometrium in the luteal phase (mean 1.0 cm thickness) can be significantly thicker than in the follicular phase (0.6 cm), and differentiation from endometrial lesions may be difficult based on thickness alone 4