The indications for fetal heart ultrasound include maternal factors, fetal factors and familial factors. Maternal factors Maternal age > 35 years. Pregnant women with precordial disease. History of pregnancy abnormalities, such as fetal death in utero, miscarriage, excessive amniotic fluid or low amniotic fluid, etc. Pregnant women have taken suspected teratogenic drugs (such as lithium oxide, dalentin, etc.) in early pregnancy or have been exposed to suspected teratogenic substances (such as radiation, etc.) during pregnancy. Pregnant women with various types of diabetes, connective tissue disease, infectious diseases (e.g. TORCH infection in early pregnancy). Pregnant women with positive anti-Ro or anti-La antibodies. Fetal factors 1. Fetal chromosomal abnormalities: autosomal 13-trisomy fetuses with congenital cardiovascular malformations up to 84%. The incidence of congenital cardiovascular malformation with autosomal 21-trisomy (Down syndrome) is 50%. 2. Fetal obstetric ultrasound screening suggests suspected cardiac malformations. 3.Fetal cardiac arrhythmia. 4.Organ malformation other than fetal heart, such as structural anomalies (hydrocephalus and renal disorders); genetic syndrome and related anomalies; non-immune edema; excessive or too little amniotic fluid; thickening of the nuchal translucency layer. 5, twin pregnancies (twin transfusion syndrome and heartless twin malformations). The risk of fetal heart disease is increased by 5-20% for pregnant women with preterm heart disease and 3.33% (1/30) for fetuses of fathers with preterm heart disease. The risk of fetal heart disease in a second pregnancy is 1-5% for those who have a history of fetal heart disease or a history of pregnancy with an affected child, and the risk of fetal heart disease in a third pregnancy increases to 10-20% if the second child also has preterm heart disease.