Which of the following conditions has the highest chance of miscarriage?

Turner Syndrome is associated with a high rate of miscarriage, particularly in pregnancies where the fetus is affected by this condition. It occurs when there is a complete or partial absence of one of the two X chromosomes in females. Statistically, around 98% of fetuses with Turner Syndrome do not survive to term, making miscarriages very common in pregnancies affected by this condition.

While Patau Syndrome (Trisomy 13), Edward's Syndrome (Trisomy 18), and Down Syndrome (Trisomy 21) are also associated with increased rates of miscarriage and congenital anomalies, their rates are comparatively lower than those seen in Turner Syndrome. Patau and Edwards syndromes have higher postnatal mortality as well, but a significant number of affected pregnancies may be carried to term, albeit often with severe disabilities. Down Syndrome, while it has significant implications for development and health, is not typically associated with such high rates of miscarriage as Turner Syndrome.

Thus, given the data regarding miscarriage risk, Turner Syndrome stands out as the condition with the highest chance of miscarriage.