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Serum biochemistry

Screening for trisomy 21

 

Trisomic pregnancies are associated with altered maternal serum concentrations of various feto-placental products.

Screening in the second trimester by maternal age and various combinations of total or free ß-hCG, AFP, uE3 and Inhibin A can identify 56-71% of trisomy 21 pregnancies for a false positive rate of 5%.

Screening in the first trimester by a combination of maternal age, fetal NT, FHR and serum free ß-hCG and PAPP-A identifies about 90% of trisomy 21 pregnancies for a false positive rate of 3%.