Abnormal thickening of the endometrium is considered for three main reasons: first, pregnancy-related. Possible pregnancy-related causes: 1. Intrauterine pregnancy. Endometrial thickening in intrauterine pregnancy occurs mainly because the pregnancy is relatively short and the gestational sac is not yet visible, a condition that slowly becomes visible as the pregnancy grows. 2. It is possible that the pregnancy is ectopic. Most early ectopic pregnancies show thickening of the endometrium and there may be a mass in the ovary or adnexal area, in which case the possibility of ectopic pregnancy should be highly suspected. Second, functional lesions are mainly considered. The main consideration is abnormal endometrial hyperplasia, which is mostly an endocrine disorder. Thirdly, we should consider that there may be organic lesions, such as endometrial polyps and endometrial tumors, which can cause abnormal thickening of the endometrium.