To date, various clinical and animal tests have shown that ultrasound is safe for the fetus. Ultrasound in early pregnancy is critical because the percentage of spontaneous abortions in early pregnancy is about 10-15%. Ultrasound at 7-8 weeks of pregnancy can clarify whether the embryo is located in the uterus, whether there are fetal buds and fetal heart, so as to promptly diagnose ectopic pregnancy, embryonic arrest, hyperemesis gravidarum, and other abnormalities; it can also check the gestational week by the size of the fetal buds, which is especially important for pregnant women who have irregular menstruation and can’t remember the last menstruation; moreover, only ultrasound during early pregnancy can help to identify monozygotic twins and dizygotic twins in a twin pregnancy. All these results play a crucial role in future pregnancy care and delivery.