<prompt> Best sonological marker for diagnosis of downs in 1st trimester:Nuchal translucencyFetal heartMicrocephalyPolyhydramnios  <response>: Ans-A Ref: Duttas Text Book of Obstetrics, 7th edition, pg 106. Williams Obstetrics, 23rd edition. Explanation: Antenatal Screening for Downs syndrome First-trimester screening for downs syndrome includes NT nuchal translucency, PAPP-A, hCG Nuchal translucency 3.5 mm is significant. It is done at 11-14 weeks Detection rate- 79-87 Triple test and quadruple tests are done in second trimesier at 15-20 weeks Triple test: hCG, AFP, unconjugated estriol. Quadruple test: triple test inhibit! Integrated test: first trimester screening quadruple test MSAFP, UE3, HCG, Inhibin A in downs syndrome. USG markers of Downs syndrome fetus soft tissue markers Nuchal fold thickening Mild renal pelvis dilatation Echogenic intracardiac focus Echogenic bowel Short femur Short humerus DOWNs syndrome around 40 congenital heart disease -Complete atrioventricular septal defect CAVSD - 37 percent -Ventricular septal defect VSD - 31 percent -ASD - 15 percent -Partial atrioventricular septal defect PAVSD - 6 percent -Tetralogy of Fallot TOF - 5 percent -PDA - 4 percent -Miscellaneous - 2 percent Reference: Uptodate; largest population based study on Downs done from UK 