Prenatal ultrasonography is the application of the physical properties of ultrasound to image the fetus and its appendages, and is the most common, non-invasive and reproducible method to understand the general morphology of the main anatomical structures of the embryo and fetus. The use of ultrasound is beneficial to further improve the quality of the birth population. However, due to the limitations of ultrasound technology, prenatal ultrasonography cannot detect all abnormalities or make predictions about the subsequent development of the fetus, so ultrasound diagnosis cannot be equated with clinical diagnosis. I. Indications Confirmation of intrauterine pregnancy, clinical suspicion of ectopic pregnancy, assessment of gestational week, diagnosis of multiple pregnancy, understanding of embryonic or fetal condition (survival or death), finding the cause of bleeding in early pregnancy, finding the cause of lower abdominal pain in early pregnancy, assessing maternal pelvic mass, uterine malformation, clinical suspicion of gravidity, and auxiliary chorionic villus biopsy. 1. Gestational sac, to observe the location, number, size and morphology of the gestational sac. 2.Yolk sac, observe the size and morphology of the yolk sac. 3.Measurement of the head-rump length and observation of fetal heartbeat. 4.Uterus and bilateral adnexa, observe the morphology and myometrial echo of uterus, the relationship between uterus and gestational sac, and the presence of bilateral adnexal masses. It is recommended to keep the following ultrasound images Longitudinal and transverse sections of the uterus including the gestational sac, and measurement of the embryo length or head-rump length. The head-rump length should be measured in the maximum long-axis view of the embryo or in the median sagittal view of the fetus, when the fetus is in a naturally extended position without hyperextension or hyperflexion. Ultrasound cannot diagnose all ectopic pregnancies. Currently, the detection rate of ectopic pregnancy by transabdominal ultrasound ranges from 40.9% to 76.0%, and the detection rate by transvaginal ultrasound ranges from 75.6% to 95.8%, as reported in the domestic literature.