The term fetal nuchal translucency (NT) refers to the hypoechoic area between the fetal neck skin and the overlying cervical spine tissue seen on ultrasound. The accumulation of fetal neck fluid can be observed by ultrasound during 10-14W of pregnancy, and after 14W, the fetal lymphatic system is fully developed and can drain the lymphatic fluid away. And NT disappears. When NT is as large as 3mm, chromosome should be checked and if karyotype is normal, fetal heart malformation should be excluded by ultrasound at 22-32 weeks of gestation.