How to check for endometrial receptivity on ultrasound (USG)?

Assessing Endometrial Receptivity on Ultrasound

Endometrial receptivity on ultrasound is assessed primarily through measurement of endometrial thickness in the mid-sagittal plane, evaluation of endometrial morphology/pattern, and assessment of subendometrial and uterine artery blood flow using color Doppler imaging. 1

Proper Measurement Technique

Endometrial Thickness Measurement

• Position the transvaginal probe to obtain a true longitudinal (sagittal) view of the uterus, ensuring you are in the midline plane. 1
• Measure the double-layer thickness (anterior plus posterior endometrium) at the thickest portion, ensuring the measurement is perpendicular to the endometrial-myometrial interface. 1
• Include both anterior and posterior layers of the endometrium in a single measurement. 1

Common Technical Errors to Avoid

• Do not measure in an oblique plane rather than true sagittal plane, as this falsely increases thickness. 1
• Avoid including adjacent myometrium in the measurement. 1
• Do not measure only a single layer of the endometrium. 1
• Ensure you are measuring at the thickest portion, not at a random location. 1
• If intrauterine fluid is present, measure and report it separately from endometrial thickness. 1

Endometrial Morphology Assessment

Pattern Classification

• Evaluate the endometrial pattern/morphology, as this correlates with receptivity—a trilaminar (triple-line) pattern is generally associated with better receptivity. 2
• The endometrial classification differs significantly between pregnant and non-pregnant groups in assisted reproduction. 2

Doppler Assessment of Endometrial Blood Flow

Subendometrial Blood Flow

• Use color Doppler to evaluate subendometrial blood flow patterns, as the presence and characteristics of subendometrial vascularity are important indicators of endometrial receptivity. 1, 2
• Classify subendometrial blood flow type, as this classification shows statistical differences between successful and unsuccessful implantation. 2
• The presence of subendometrial flow is associated with successful implantation in stimulated cycles. 3

Spiral Artery Parameters

• Measure the pulsatility index (PI) and resistance index (RI) of spiral arteries within the endometrium—lower values indicate better receptivity. 2
• Spiral artery blood flow parameters can be effective indices for evaluating endometrial receptivity. 2
• In successful pregnancies, spiral artery RI and PI are significantly lower compared to unsuccessful outcomes. 2

Uterine Artery Doppler

• Measure the RI and PI of both uterine arteries, as well as the peak systolic velocity/end diastolic velocity (S/D) ratio. 2
• The sum of S/D of both uterine arteries has a cutoff value of 14.47 for predicting pregnancy success. 2
• Lower uterine artery impedance (lower RI and PI) is associated with better endometrial receptivity. 3

Three-Dimensional Ultrasound Parameters (When Available)

Volumetric Assessment

• Measure endometrial volume using 3D ultrasound, as it has the highest reproducibility among ultrasonographic parameters for endometrial receptivity. 4
• Endometrial volume is significantly lower in recurrent miscarriage patients compared to normal pregnancy groups. 5

3D Power Doppler Indices

• Calculate the vascularization index (VI), flow index (FI), and vascularization-flow index (VFI) using 3D power Doppler—these provide comprehensive assessment of endometrial vascularity. 5
• VI, FI, and VFI in the midluteal phase are significantly lower in recurrent miscarriage patients. 5
• 3D power Doppler ultrasound is a more comprehensive and sensitive method for evaluating endometrial receptivity than 2D ultrasound alone. 5

Timing of Assessment

• Perform the assessment during the mid-luteal phase (window of implantation), typically 7-10 days after ovulation or timed with urinary LH testing. 6, 5
• This timing corresponds to the period when the endometrium should be maximally receptive. 7

Clinical Context and Limitations

Important Caveats

• While ultrasound can assess structural and vascular parameters, it cannot definitively determine implantation potential—molecular markers like the endometrial receptivity array (ERA) are superior for defining the personalized window of implantation. 7
• The presence of leiomyomas or adenomyosis may limit visualization and accurate measurement of the endometrium. 7, 8
• Neither endometrial thickness alone nor morphology can definitively differentiate between those who will achieve clinical pregnancy in all cases. 6

When to Consider Additional Testing

• If ultrasound findings are inconclusive or there is a focal endometrial abnormality, consider sonohysterography for further characterization. 7, 9
• MRI with diffusion-weighted imaging should be considered when ultrasound is inconclusive or the uterus is incompletely visualized. 7, 8