Sequencing methods and compositions for prenatal diagnoses

A method for preparing a sequencing library from a test sample comprising nucleic acid molecules, wherein said nucleic acids molecules are human cell-free DNA (cfDNA) molecules, wherein the method comprises the consecutive steps of end-repairing, dA-tailing and adaptor ligating said nucleic acids molecules, wherein said consecutive steps exclude purifying the end-repaired products prior to the dA-tailing step and exclude purifying the dA-tailing products prior to the adaptor-ligating step, and wherein said consecutive steps are performed in less than 1 hour.