The thickness of the endometrium is between 9-11mm, with an average of about 10mm, which is the normal thickness of the ovulatory lining and allows for a normal pregnancy. If the ovulatory lining is too thin or too thick, it can affect the implantation of the fertilized egg and affect normal pregnancy. If the endometrium is too thin, and the thickness of the endometrium at the time of ovulation is less than 8mm, the fertilized egg cannot implant normally, and it is very easy to lead to biochemical pregnancy, that is to say, the fertilized egg does not implant and there is a hidden miscarriage. If the endometrium is too thick during ovulation, more than 12mm, the fertilized egg can’t implant, it is considered to be related to the low level of progesterone in the body, so that the endometrium in proliferative stage doesn’t transform to secretory stage, which is not conducive to the implantation and development of the pregnant egg.