<prompt> The best way of diagnosing Trisomy 21 during second trimester of pregnancy is:Triple marker estimationNuchal skin fold thickness measurementChorionic villus samplingAmniocentesis  <response>: The main use is in diagnosing chromosomal disorders like trisomy 21.Amniotic fluid cells are cultured and karyotyping done,which may take up to 3 weeks refer pgno:502 sheila textbook of obstetrics 2 nd edition 