Prenatal Diagnosis of Chromosome Abnormalities: A 13-Year Institution Experience

To analyze trends in screening and invasive prenatal diagnosis of chromosome abnormalities (CA) over a 13-year period and correlate them to changes in the national prenatal screening policy.

We retrospectively reviewed Down syndrome (DS) screening tests and fetal karyotypes obtained by prenatal invasive testing (IT) in our fetal medicine unit between January 1999 and December 2011.

A total of 24,226 prenatal screening tests for DS and 11,045 invasive procedures have been analyzed. Over a 13-year period, utilization of non-invasive screening methods has significantly increased from 57% to 89%. The percentage of invasive procedures has declined from 49% to 12%, although the percentage of IT performed for maternal anxiety has increased from 22% to 55%. The percentage of detected CA increased from 2.5% to 5.9%. Overall, 31 invasive procedures are needed to diagnose 1 abnormal case, being 23 procedures in medical indications and 241 procedures in non-medical indications.

Our experience on screening and invasive prenatal diagnostic practice shows a decrease of the number of IT, with a parallel decline in medical indications. There is an increasing efficiency of prenatal screening program to detect CA. Despite the increasing screening policies, our population shows a growing request for prenatal IT. The a priori low risk population shows a not negligible residual risk for relevant CA. This observation challenges the current prenatal screening strategy focused on DS; showing that the residual risk is higher than the current cut-off used to indicate an invasive technique.