Various diagnostic methods are available for the prenatal diagnosis of Tay-Sachs disease, aimed at determining the presence of the affected gene in the fetus:

1. Chorionic Villus Sampling (CVS): Genetic testing is performed on a tissue sample taken from the placenta, usually between the 10th and 13th weeks of pregnancy, either vaginally or abdominally.
2. Amniocentesis: Genetic analysis is performed on a sample of amniotic fluid surrounding the fetus, usually taken between the 15th and 20th weeks of pregnancy.

Samples obtained through these procedures are subjected to genetic tests to detect the specific gene mutations causing Tay-Sachs disease.