Endometrial Thickness

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 14, 2026

Endometrial thickness is the measurement of the uterine lining obtained by transvaginal ultrasound, assessed at defined points in the menstrual cycle to evaluate implantation potential. A trilaminar (three-layer) pattern in the preovulatory phase indicates coordinated estrogen stimulation of the endometrium. Thickness below an adequate preovulatory range is associated with reduced implantation potential, though exact thresholds vary by population and cycle type.¹

Causes of thin endometrium include prior uterine instrumentation (dilation and curettage, hysteroscopic procedures), intrauterine adhesions (Asherman syndrome), estrogen deficiency, reduced uterine blood flow, and chronic infection. When the clinician identifies thin endometrium, the question is: why? Measurement alone does not answer that question.

Endometrial assessment belongs alongside ovulation timing, hormonal evaluation, and uterine cavity evaluation, not as a standalone number. A normal thickness does not exclude poor receptivity, and low thickness may resolve when the underlying hormonal or anatomic cause is addressed. The window of implantation depends on more than thickness alone, including progesterone-driven secretory transformation of the endometrium after ovulation.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.