It's true. Chromosome #s are very high-yield for certain diseases.
Down's = 21
Edward's = 18
Patau's = 13
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Aside from the above, I'd say the highest of the high-yield is:
Huntington's = 4
Marfan's = 15
Cystic fibrosis = 7
Most common cause of 1st-trimester spontaneous abortions = trisomy 16