The endometrium of 17mm depends mainly on the time of day the test was done. If the endometrium of 17mm is detected before menstruation, it is also normal. As long as the thickness of the endometrium can reach 9mm or more during ovulation, then after sex, the sperm and egg will unite to form a fertilized egg, which will go to the uterine cavity to be laid, and then pregnancy will occur. Therefore, the thickness of the endometrium changes with the menstrual cycle. When the menstruation is just clean, the endometrium is relatively thin; during the ovulation period, the endometrium is relatively thickened. The uterine lining reaches its thickest during the premenstrual period and will be thicker if you are pregnant. So it is normal to have a successful pregnancy with 17mm endometrium.