Increased parity and risk of trisomy 21. Study measured prevalence of Down's syndrome at birth, not incidence.
Pharoah
P O
PO
D004314:Down Syndrome / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D010298:Parity; D011247:Pregnancy; D015995:Prevalence