Which is the MOST appropriate gestational age for performing amniocentesis?

Amniocentesis is ideally performed between 14-16weeks of gestation. Early amniocentesis can be carried out at 12-14 weeks under ultrasonographic guidance. The fetal cells so obtained are subjected for cytogenetic analysis. Fetal fibroblasts and fluid for biochemistry are used for study. Chorionic villus sampling : is carried out transcervically between 10 - 12 weeks and transabdominally from 10 weeks to term. Trophoblast cells are used for study. Cordocentesis: Is done between 18-20 weeks of gestation. Fetal WBCs are used for study. Ref: Textbook of Obstetrics By DC Dutta 6th edn page 107-8.