<prompt> At 35years Maternal age-related risk for Down syndrome in singleton pregnancy at midtrimester is1 in 311 in 691 in 1491 in 250  <response>: Maternal Age-Related Risk for Down Syndrome at Midtrimester in Singleton PregnanciesAgeMidtrimester351250371149401694115342141431314412545119Ref: Williams Obstetrics; 25th edition 