Combine test (between the 11 th and 14th weeks of gestation) and triple test (between the 16
th and 18th weeks of gestation) are being used for trisomy 21 and trisomy 18 screening. We have
investigated the precision of fetal nuchal translucency (NT), free β HCG and pregnancy associated protein
of Pregnancy - A (PAPP- A) measurements in maternal serum and the effects of their precision to the risk
evaluation results of the patients.
Materials and Methods: To measure analytic repeatibility, 3 different serum pools have been prepared,
and 5 consecutive measurements were done from these serum pools. For NT measurement, 5
separate experienced obstetricians have measured NTÔs of 9 patients. The effects of the results from
these separate measurements on the first trimester test results have been investigated. While studying
the serum pools, IMMULITE® Free BetaHCG and IMMULITE® PAPP-A kit (Siemens Medical Solutions
Diagnostics Limited, UK) for free β HCG and for PAPP-A have been used. In risk evaluation, the prenatal
screening program (PRISCA typolog Software Gmbh, Hamburg) has been utilized.
Results: The same day repeatibility results (min - max %CV values) 3.9-8.6%, 4.2-7.0% and
respectively 4.03-17.6% for HCG, PAPP-A and NT have been found as. When the end effect of
thesebfree variations to the first trimester risk has been calculated, (using the three separate pools of
serum samples), influences of 0-16.3%, 0-0.8%, 0-16.4% for free HCG results, 0-9.5%, 0-34.6%,
8-17.1% for PAPP- A results and 27.4-37%, 24.3-35.1%, 50.7-57.2% for NT measurements were found β
Conclusion: While the analytic performances are within the acceptable ranges, the variations have
been found to influence the end risk calculation significantly. The end results are not influenced in
the low risk group, but in high risk population and in advanced maternal age groups, it causes the
final results that could effect the clinical decision making These results once again showed us that,
the analytic performance must be kept in optimum for the first trimester tests. Very strict internal and
external quality control programs are a must. NT certification is critical therefore a solid training and
definitive certification is crucial.