chromosomal abnormalities were detected in 2.4 per cent of the 2404 pregnancies tested because of advanced maternal age ( greater than or equal to 35 years ) , in 1.2 per cent of 240 monitored because of prior trisomy 21 and in 9.1 per cent of 55 examined for other cytogenetic indications .
C0008625
chromosomal abnormalities
C0013080
trisomy 21