Endometrial thickness is typically considered favorable for embryo transfer within which range?

• A. Approximately 7–12 mm
• B. Less than 5 mm
• C. Greater than 15 mm
• D. Any thickness is equally favorable

Answer: (A)

Endometrial thickness reflects how receptive the lining is to an embryo. In most embryo transfer cycles, a thickness of about 7 to 12 millimeters is associated with the best implantation and pregnancy rates. If the lining is too thin—below roughly 7 mm, and especially under 5 mm—the endometrium may be insufficiently developed with reduced blood flow and glandular activity, making implantation less likely. If it’s too thick—around or above 15 mm—it can indicate excessive estrogen exposure or edema, and outcomes tend to be poorer. Therefore, the 7–12 mm range is considered the most favorable window for embryo transfer.