A thin endometrium can have a negative impact on pregnancy. To determine the thickness of the endometrium, an ultrasound examination should be performed around day 20 of the menstrual cycle. If the endometrium is less than 7 mm, it is thin and it is difficult for a fertilized egg to successfully implant in the endometrium. Moreover, even if the egg is successfully implanted and the pregnancy is successful, the placenta is attached to the endometrium and the inflammatory factors are likely to cause miscarriage. After the placenta has been perfected, it may also lead to late miscarriage and even fetal growth restriction due to the unfavorable factors of placental attachment. Therefore, a thin endometrium has a negative impact on pregnancy, but this is not absolute, there are times when a thin endometrium is accompanied by the possibility of a normal pregnancy.