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One research concludes that in a postmenopausal woman without vaginal bleeding, if the endometrium measures more than 11 mm, then a biopsy should be considered as the risk of cancer is 6.7%.
Whereas if the endometrium measures less or equal to 11 mm a biopsy is not needed as the risk of cancer is extremely low.
Thickness may vary from time to time. However, if you have a family history of cancer you can go for biopsy.
For further information consult an obstetrician and gynaecologist online --> https://www.icliniq.com/ask-a-doctor-online/obstetrician-and-gynaecologist