The present disclosure provides methods for determining the ploidy status of an embryo at a chromosome from a sample of DNA from an embryo. The ploidy state is determined by sequencing the DNA from one or more cells biopsied from the embryo, and analyzing the relative amounts of each allele at a plurality of polymorphic loci on the chromosome. In an embodiment, the ploidy state is determined by comparing the observed allele ratios to the expected allele ratios for different ploidy states. In an embodiment, the DNA is selectively amplified at a plurality of polymorphic loci by targeted sequencing. In an embodiment, the mixed sample of DNA may be preferentially enriched at a plurality of polymorphic loci in a way that minimizes the allelic bias.