Prenatal diagnostic testing and Down syndrome in Victoria 1992-2002

Objective: To describe patterns of uptake of prenatal diagnostic testing and prenatal detection rates for Down syndrome in Victoria with regard to maternal age and prenatal screening practices. Methods: Analysis of routinely collected statewide datasets for 1992 to 2002, containing detailed information on all prenatal diagnoses, births and birth defects. Results: Utilisation of prenatal diagnosis in women less than 37 years has increased significantly (p<0.0001), whereas in older women it has fallen from 65.1% in 1996 to 42.7% in 2002. The overall proportion of diagnostic tests prompted by an increased risk screening test result has increased five-fold over 11 years to 35.4% in 2002 (p<0.0001). Almost 6% of diagnostic tests done in 2002 detected a fetal chromosome abnormality, compared with 3.0% in 1992. Prenatal detection of Down syndrome has increased in women less than 37 years with approximately 70% of cases now diagnosed prenatally (p<0.0001). A smaller non-significant increase (from 67% to 82%) in prenatal detection of Down syndrome was observed among older women. Conclusions: The widespread use of prenatal screening for Down syndrome has changed the demographic profile of women having prenatal diagnosis in terms of their age. An increasing number and proportion of younger women and fewer older women are having prenatal diagnosis. The declining figures for diagnostic testing in older women have not had an impact on prenatal detection rates for Down syndrome. Implication: Current prenatal screening practices provide a more effective risk assessment for Down syndrome and indication for prenatal diagnosis than advanced maternal age alone.