Triploidy syndrome is a condition in which there is an extra set of haploid chromosomes than normal diploidy, with three sex chromosomes and a total chromosome count of 69. Triploidy syndrome is the most common polyploidy diagnosed prenatally. 99% of triploid fetuses are not born alive and most of them abort at 10-20 weeks of gestation, accounting for approximately 10% of spontaneous abortion cases in early pregnancy. Mosaic triploids can survive for a longer period of time. There are three karyotypes of triploidy, namely 69XXY, 69XXX, and 69XYY, with proportions of 60%, 37%, and 3%, respectively. The mechanisms of triploidy occurrence mainly include double male fertilization and double female fertilization. Characteristic manifestations include large placenta-like gravidity, dysgenesis, and third and fourth juxtaposition. Surviving children usually show severe intrauterine growth restriction, disproportionate head circumference and abdominal circumference, and very small abdominal circumference. There is cranial vault hypoplasia with large posterior fontanelle; wide eye spacing and small eyes; low nasal bridge; low and malformed ears; and small jaws. Through the palm; characteristic clubfoot, third and fourth finger syndactyly; congenital heart disease, including atrial septal defect. Male hypospadias, hypospadias, cryptorchidism. There is no specific treatment available. The miscarriage rate of triploidy syndrome is 99%. Most of the few survivors are mosaic, and most of them die within one hour after delivery, especially double female fertilized triploidy, and those who can survive for one month are rare; double male fertilized triploidy can survive relatively short-term, and so far, the longest survivor is 40 weeks. Prevention: 1. Be alert to the emergence of malignant gravida when you have another pregnancy, detect changes in maternal serum hCG during pregnancy, regular ultrasound examination, and close follow-up. 2. When fetal growth restriction, placental thickening and small blister-like changes occur during pregnancy, attention should be paid to differentiate them from general fetal restriction, placental abruption and complete gravida caused by paternal uniploidy. 3. When triploidy syndrome is highly suspected, amniotic fluid cell karyotyping is recommended to confirm the diagnosis and terminate the pregnancy at the earliest.