chromosome abnormalities , especially trisomies 13 , 18 , and 21 , and sex chromosome aneuploidies , increase exponentially with maternal age starting in the 30s , reaching levels of 1.4 per cent at age 35 , 1.9 per cent at 40 , and 8.9 per cent at 45 , according to amniocentesis data .
C0008625
chromosome abnormalities
C0152095
trisomies 13