<s>[INST] context: Noninvasive prenatal diagnosis of hemophilia by microfluidics digital PCR analysis of maternal plasma DNA.Haemophilia is a bleeding disorder with X-linked inheritance. Current prenatal diagnostic methods for haemophilia are invasive and pose a risk to the fetus. Cell-free fetal DNA analysis in maternal plasma provides a noninvasive mean of assessing fetal sex in such pregnancies. However, the disease status of male fetuses remains unknown if mutation-specific confirmatory analysis is not performed. Here we have developed a noninvasive test to diagnose whether the fetus has inherited a causative mutation for haemophilia from its mother. The strategy is based on a relative mutation dosage approach, which we have previously established for determining the mutational status of fetuses for autosomal disease mutations. In this study, the relative mutation dosage method is used to deduce whether a fetus has inherited a haemophilia mutation on chromosome X by detecting whether the concentration of the mutant or wild-type allele is overrepresented in the plasma of heterozygous women carrying male fetuses. We correctly detected fetal genotypes for haemophilia mutations in all of the 12 studied maternal plasma samples obtained from at-risk pregnancies from as early as the 11th week of gestation. This development would make the decision to undeake prenatal testing less traumatic and safer for at-risk families. [/INST] question: Prenatal diagnosis of haemophilia is best done by | options: A: PCR B: Linkage analysis C: Cytometry D: Microarray | answer: A </s>