The best time for amniocentesis is usually 16-24 weeks of gestation, with the optimal gestational week being 20-22 weeks. Amniotic fluid cells are derived from fetal cells and fetal membrane cells, and the number of fetal cells is a key factor in the success of the culture. If the number of fetal cells obtained by amniocentesis is not guaranteed too early or too late, the success rate of culture may be affected. If the culture fails, a repeat amniocentesis will be required. If the placenta is located in the anterior wall of the uterus and intraoperative access is found to be difficult, it may be necessary to cross the placenta causing bleeding, it is recommended that the puncture be prolonged appropriately and the timing of the puncture be delayed by 1-2 weeks.