<prompt> Prenatal diagnosis at 18 - 20 weeks of pregnancy can be performed using all of the following, except:Amniotic fluidMaternal bloodChorionic villus samplingFetal blood  <response>: Prenatal diagnostic techniques for fetal abnormalities Chorionic villus sampling - done at First trimester10-13th weeks Amniocentesis - done at second trimester16-18th weeks Percutaneous umbilical blood sampling cordocentesis - done after 18 weeks. Non invasive Prenatal Test: Maternal serum is taken for evaluation of Downs syndrome other chromosomal and genetic disorders. All pregnant female have cell free fetal DNA in their circulation which can be used to assess fetal karyotype. Source of cell free DNA is apoptosis of placental cells. This can be done anytime after 9 weeks 