Quality assured first trimester screening for aneuploidies
Screening for Down syndrome in the first trimester using the combination of biochemical placental markers free beta hCG and pregnancy associated plasma protein-A (PAPP-A) with ultrasound nuchal translucency measurement has become the standard of prenatal care. Performance parameters established by the Fetal Medicine Foundation (FMF), London have been adopted by most screening laboratories. Many biochemistry laboratories, however, do not have the resources to quality assure the efficacy of testing systems. Our laboratory has incorporated screening with cytogenetics and molecular genetics enabling the constant “live-time” monitoring of performance parameters, essential criteria to the establishment of domestic variations and verification of laboratory assay performance.
To date in excess of 60,000 cases have been assessed by our unit. Quality assurance by cross referencing with cytogenetics outcomes has confirmed our performance parameters for trisomy 21 (T21) (n=135 cases) at 90% with a false positive rate of 5%. In addition, biochemical profiles for trisomy 18 (n=36), trisomy 13 (n=14) and triploidy (n=12) have been developed. Biochemical profiles for cases of fetal demise in the first trimester also demonstrate clear patterns consistent with these aneuploidies. Approximately 50% of aneuploidies were identified in women less than 37 years of age. Prior to the advent of first trimester screening, this group of patients would not have been offered invasive testing and the positive identification of an affected pregnancy.
Screening performance at Sydney Genetics is based upon the integration of cytogenetics and molecular DNA testing. Real time quality assurance allows vigilance of efficacy and monitoring of performance.