Amniocentesis is necessary for fetal ventricular septal defect at 21 weeks. Fetal ventricular septal defect is a common fetal cardiac anomaly during pregnancy, according to the site of the defect, it is divided into three types: perimembranous, subpulmonary and muscular defects, and according to the size of the defect, it is divided into small defects (<0.5cm), medium defects (0.5-1cm), and large defects (>1cm). If fetal cardiac ultrasound during pregnancy suggests the presence of ventricular septal defect, amniocentesis is performed first for prenatal diagnosis to rule out fetal chromosomal abnormalities. Fetal ventricular septal defects generally do not affect intrauterine development, and the presence or absence of symptoms after birth is related to the size of the defect. If detected during pregnancy, in addition to obstetrics to rule out other fetal cardiac anomalies and chromosomal anomalies, the pediatric surgery department can be consulted for questions related to postnatal fetal surgery.