It is best to get pregnant when the thickness of the endometrium is between 8 and 15 mm, too thick to get pregnant and too thin to get pregnant. Because the endometrium changes gradually throughout the menstrual cycle, if the endometrium is more than 8mm during ovulation, it is normal and the possibility of pregnancy is higher. If it is too thin, the fertilized egg cannot implant into the endometrium and it is very difficult to get pregnant. If it is too thick, the fertilized egg will not reach the basal layer after implantation into the endometrium, and the fertilized egg will lose nutrition and miscarriage will occur, making it difficult to get pregnant.