Introduction New national guidelines for Down's syndrome screening will impact on prenatal diagnostic services and robust cytogenetic services are essential to meet the demands for rapid and accurate diagnosis. Our objectives were to determine the success rates of rapid aneuploidy detection (RAD) and long-term culture (LTC) and compare them to national standards to assess the quality of service provision.

Methods Retrospective analysis of computer records from 1 May 1999 to 30 September 2009 was performed for amniotic fluid samples (AFS) and chorionic villus samples (CVS). RAD results were compared to LTC for each patient and success rates of each were determined. Discordance rates between RAD and LTC were calculated and discrepant results analysed to determine the nature of discrepancy.

Results 10 133 AFS and 2083 CVS were analysed. Success rates were >99.9% and 96.4%, respectively which meet national standards for cytogenetic laboratories. RAD was performed in 7641 (75.4%) with 98.3% success and 1992 (95.2%) with 95.1% success for AFS and CVS, respectively. The rate of discrepancy between RAD and LTC for abnormalities of chromosomes 13, 18, 21, X and Y as a percentage of total abnormal results were 0.9% for AFS and 1.2% for CVS. The proportion of all abnormal chromosomes missed by RAD but not LTC was 16% and 1.7% for AFS and CVS, respectively.

Conclusion The North Trent Cytogenetic Service achieves national standards for processing of prenatal diagnostic samples required to meet the demands of the new screening programme. Large studies are required to resolve whether cytogenetic screening services should be based solely on RAD without follow-on LTC.