Objectives: To summarize the experience and evaluate the performance of the Hat Yai maternal serum screening (MSS) program.
Setting: The Hat Yai MSS program between 16 February 2003 and 11 March 2004.
Material and Method: The uptake of screening was 999 in 1,040 women (96.0%), between 14 to 20 weeks of gestation with the triple markers: Alpha-fetoprotein (AFP), human Chorionic Gonadotropin (hCG), and unconjugated Estriol (uE3) by Immulite chemiluminescent immunoassay system, Diagnostic Product Corporation (DPC). The risk cut-off for Down’s syndrome is one in 250 or greater, based on software for prenatal Down’s syndrome risk calculation, by Prisca 3.5 DPC.
Results: There were 119 in 999 cases (11.9%) of the triple test positive. Amniocentesis had been performed on voluntary basis, and the uptake rate of amniocentesis following a positive Down’s syndrome screening was 104 in 119 cases (87.3%). Based on clinical diagnosis of Down’s syndrome in the newborns of non-amniocentesis mothers, assuming that normal looking babies were not Down’s syndrome, the sensitivity (SENS), specificity (SPEC), positive predictive value (PPV), and negative predictive value (NPV) of all chromosomal abnormalities were 85.7%, 88.6%, 5.0%, and 99.8% respectively. The false positive rate was 113 in 992 cases (11.4%). Whereas, the SENS, SPEC, PPV, and NPV of Down’s syndrome were 100%, 88.4%, 3.4%, and 100% respectively. The false positive rate was 115 in 995 cases (11.6%). The mean level, median level, and multiple of median (MoM) of triple markers were demonstrated.
Conclusion: The Down’s syndrome screening is a systematic application of a test to identify subjects at increased risk of a specific disorder, of course it is not diagnostic, but to benefit making decision regarding further amniocentesis. The sensitivity of Prisca 3.5 software was satisfactory but false positive rate was remarkably high. It needs further standardization with adjusted MoM values.

Keywords: Triple test, Second trimester, Down’s syndrome, Alpha-fetoprotein, Human chorionic gonadotropin, Unconjugated estriol