There are two ways to indicate whether that baby has inherited HD through analyzing a sample of fluid from around the fetus (amniocentesis), or through a sample of fetal cells from the placenta (chorionic villus sampling/ CVS)
2) Pre-Symptomatic Testing
Is usually requested by a patient whose parent is known to have HD or is suspected to have the disease but the patient doesn’t carry any symptoms or doesn’t know whether or not they carry it; this test is used to confirm or deny that the patient has HD.
3) Confirmatory Testing
Confirms if a patient who is experiencing symptoms of HD, has the disease or not. This is done by analyzing the patients karyotype (a photograph of pairs of homologous chromosomes in a cell) OR a patients pedigree chart (a flowchart that uses symbols to show the inheritance patterns of traits in a family over many generations). A pedigree chart is used because HD is a hereditary disease and a pedigree is a way to analyze how a trait "runs in the family". Doctors are able to see who was been affected by HD which helps them deduce the patients chances of having HD.
Karyotype
Pedigree Chart
Huntington's disease is inherited in an autosomal dominant fashion. The probability of each offspring inheriting an affected gene is 50%. Inheritance is independent of gender, and the phenotype does not skip generations.