A 9mm thick uterine lining is not necessarily pregnancy because after pregnancy the lining of the uterus is much thicker than 9mm, for example around 13mm it could be pregnancy, so when the uterine lining is only 9mm it is not necessarily pregnancy. If you do not have your period by the time you come to menstruation, then do the appropriate tests to find out if you are pregnant. The endometrium is normally above 1cm before menstruation, around 9mm during ovulation, and only 5-6mm when menstruation is clean.The endometrium changes with the menstrual cycle, so when the thickness of the endometrium is only around 9mm, it is possible that the endometrium is ovulating. If the endometrium is 9mm thick before menstruation, it is endometrial thinning, and you need to know what causes endometrial thinning, and then give treatment clinically.