The normal endometrium is divided into a functional layer and a basal layer. The functional layer grows and sheds every month to form menstruation, while the basal layer is not shed. One cell splits into two, one of which is still a basal layer cell, while the other becomes a functional layer cell. The endometrium undergoes cyclic changes in response to the hormonal cycle of the menstrual cycle, including three phases: the proliferative phase, the secretory phase and the menstrual phase. The endometrium, as the land where the embryo is conceived, is an important factor affecting pregnancy outcome. Let’s take a look at what the endometrium looks like and what kind of endometrium is suitable for embryo implantation from the perspective of ultrasound imaging. The thickness of the endometrium before ovulation is usually 8-13mm, 6-8mm is the thin type, 13-15mm is the thick type, <6mm may not be able to get pregnant; >15mm may have lesions such as endometrial hyperplasia. The endometrial pattern before ovulation is usually type A, which means that three lines can be seen on ultrasound, called the “three-line sign”. If there is strong echogenicity, endometrial hyperplasia or polyps cannot be excluded and should be rechecked after menstruation. If it is not type A and the three lines start to become blurred, it is called type B, which is the endometrial pattern after ovulation. There is another type of endometrium called type C. The endometrium is very echogenic and muddy, and such an endometrium is not suitable for embryo implantation. Now we all know that the endometrium should not only have the right thickness but also a beautiful morphology, so that the endometrium is fertile ground for seed germination.