Early pregnancy is manifested by menopause longer than the menstrual cycle, with early pregnancy reactions such as nausea and vomiting, and a positive urine HCG test. In patients with regular menstrual cycles, a gestational sac can be detected by transabdominal ultrasound as early as day 34 of menstruation and by transvaginal ultrasound as early as day 28 of menstruation. The purpose of ultrasound during early pregnancy: 1: to determine the pregnancy, 2: to know the site of pregnancy, and 3: to know the development of the embryo. Conception can be divided into 3 phases from egg fertilization to delivery of the fetus. 1. Ovulation phase: From the fertilization of the egg to the implantation of the egg is called the ovulation phase, which lasts about 2 weeks. Since the egg is not yet in the womb, it cannot be visualized by ultrasound.2. Embryonic phase: After the fertilized egg is in the womb, it is called the embryonic phase, which lasts about 5 weeks. After the egg has been laid, it is called the embryo, and after development, the amniotic sac and yolk sac rapidly appear. Later, the yolk sac shrinks, the amniotic cavity expands, and the embryo is suspended in the amniotic fluid, and the early gestational sac can be shown by ultrasound during this period.3. Fetal stage: from 9 weeks of pregnancy to delivery, it is called the fetal stage. 2D ultrasound during this period shows the fetal head, fetal body, umbilical cord, placenta, and other fetal structures in the uterine cavity. The gestational sac (rounded aperture with an anechoic zone in the middle) can be seen in the uterine cavity. The gestational sac, together with the peritoneum on its surface, the true metaplasm on its opposite side and the dilated cavity between the peritoneum and the true metaplasm form a double metaplastic sac echogenicity, showing a typical double ring of sac-like anechoia with a peripheral hyperechoic halo. As the gestational week increases, the yolk sac, amniotic sac, and fetal bud echoes may appear. At 5 weeks of gestation, the gestational sac occupies 1/4 of the uterine cavity, and at 10 weeks of gestation, the gestational sac occupies the entire uterine cavity. At 5 weeks of gestation, the yolk sac shows clearly and is about 3 mm in diameter. After 10 weeks of gestation, the yolk sac gradually shrinks and disappears. At 5 weeks of gestation, a hyperechoic point, called embryonic point, is visible next to the yolk sac, and there is no primitive heart tube pulsation yet. Faint primitive heart tube pulsation can be detected in the center of the fetal bud by transabdominal ultrasound at the earliest 42 days of gestation and transvaginal ultrasound at the earliest 38 days of gestation. At 7 weeks of gestation, the fetal bud is about 4 mm long, and the fetal heartbeat is obvious, and the buds of the upper and lower limbs are visible. At 8 weeks of gestation, the embryo takes human form and all parts are developing rapidly, the head, trunk and limbs are clearly visible.