Provided is a method for determining a genetic condition of a fetus, the method including: an objective region selection step of selecting an objective region for determining the genetic condition, from regions on a human genome; a step of isolating a single cell from a maternal blood sample; a step of extracting genomic DNA from the single cell; a step of performing PCR amplification on the objective region using a primer set designed so as to perform the PCR amplification on the objective region using genomic DNA extracted from the single cell as a template; and a DNA sequencing step of decoding a DNA base sequence of a PCR amplification product of the objective region, in which the primer set designed so as to perform the PCR amplification on the objective region is designed through a method for designing a primer set used for the polymerase chain reaction, the method for designing a primer set including a first stage selection step based on a local alignment score and a second stage selection step based on a global alignment score.