Ans. is b i.e. Amniocentesis In a pregnant lady with H/0 previous Down syndrome, the chances of recurrence are increased. Extensive screening should be carried out in all such females. Now in the question given - female is presenting at 18 weeks and investigation of choice is being asked which will definately be amniocentesis. At 18 weeks Screening test : quad test I Triple test. Investigation of choice : Amniocentesis. In first trimester (or 1st screening test Combined test Investigation of choice chorionic villi sampling. Screening test selectior Women presenting to ANC clinic before 14 weeks. Nuchan translucency + free phCG +PAPP-A (k/a combined test) Based on result if