Second-trimester prenatal screening for trisomy 21 using biochemical markers: a 7-year experience in one cytogenetic laboratory.

Background: Screening for trisomy 21 in the second trimester of pregnancy using biochemical markers is an established part of prenatal care in many developed countries.

Objective: The present study was aimed at determining the incidence of trisomy 21 and other chromosomal abnormalities in women undergoing prenatal chromosome analysis after a second-trimester biochemical screening.

Results: A total of 2832 karyotypes were analyzed following a positive second-trimester maternal serum screening (risk > or = 1/250) between 1998 and 2004.