Down's syndrome--factors influencing its incidence.
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D003430:Cross-Sectional Studies; D004314:Down Syndrome / Q000453:epidemiology* / Q000517:prevention & control; D005260:Female; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D011247:Pregnancy; D011296:Prenatal Diagnosis; D012307:Risk Factors; D012846:Singapore / Q000453:epidemiology