Serum biochemistry
Screening for trisomy 21
In trisomy 21 pregnancies maternal serum free ß-hCG is about twice as high and PAPP-A is reduced to about half compared to chromosomally normal pregnancies.
Performance of screening for trisomy 21 by maternal age and serum free ß-hCG and PAPP-A:
- Detection rate 65%
- False positive rate 5%