Comparison of Nicolaides' risk evaluation for Down's syndrome with a novel software: an analysis of 1,463 cases

The individual risk assessment of fetal Down's syndrome based on measurement of nuchal translucency (NT) according to Nicolaides, optionally complemented by the determination of PAPP-A and free beta HCG has progressively supplanted other search strategies for fetal aneuploidies. It could be shown that this diagnostic strategy equally detects other numeric aneuploidies at a comparable rate. A positive test result is also predictive for the presence of a fetal malformation. In this field, several computer programs are available for clinical use. The objective of our study was to re-evaluate the first consecutive 1463 NT-risk calculations determined by Nicolaides' method and to compare the risk calculation to the JOY software (NT-risk calculation module, JOY Patient Database) introduced in 2002.

At the Department of Obstetrics and Gynecology, Hannover Medical School, 1463 consecutive complete data sets comprising first trimester screening performed between May 2, 2000 and June 26, 2003 and corresponding fetal outcome were analysed using risk assessment based on the Nicolaides method (PIA Fetal Database NT-Module) and compared with the risk evaluation as determined by the JOY software (JOY Patient Database NT module). A risk exceeding 1:300 was considered to indicate the need for further invasive testing. In a first step, only cytogenetically detectable chromosomal aberrations were analysed. Then, a second evaluation including fetal malformations was performed.

Among the 1463 cases, 1445 (98.77%) fetuses revealed to be cytogenetically healthy. Both softwares showed identical detection rates at the genetic and somatic level:13 cases of Down-Syndrome (0.89%), 2 cases of trisomy 18 (0.14%), one case of triploidy, one Turner-Syndrome, one Klinefelter-Syndrome (0.07% each) were detected. A positive test result was found in 15 cases ending in a spontaneous abortion, intrauterine death or peripartum death (1.03%) and in 22 cases of fetal malformation (1.50%). At the level of genetic detection the test positive rate dropped from 92 (PIA) to 71 (JOY) (-22.8%). At the level of combined adverse outcome the test positive rate was reduced from 100 (PIA) to 76 (JOY) (-22.0%), thus yielding in a marked improvement of the characteristic test performance parameters.

The novel, recently developed JOY software package allowed reliable evaluation of the risk for aneuploidy with increased specificity whereas sensitivity was unchanged. Our data suggest an improvement of the screening for aneuploidy when using this novel software: With an identical detection rate, the number of unnecessary invasive measures may be reduced.