Second trimester Down syndrome serum screening--results from a pilot study

The results from a pilot prospective study--second trimester Down syndrome [DS] serum screening between 15 and 21 w.g. with two markers (alpha-fetoprotein and free bb-hCG)--were summarised. Sensitivity, false-positive rate [FPR], positive predictive value [PPV] of the screen positive and negative predictive value [NPV] of the screen negative result for the sbgroups II and below 35 years of age were analysed. The uptake for invasive prenatal testing in screen positive patients and the percentage of terminated pregnancies with prenatally diagnosed DS fetuses as well as the ratio "lost unaffected pregnancies/1 DS fetus diagnosed antenatally" were also calculated. High sensitivity of the DS serum screening was achieved--75% and 87.5% in the subgroups below and II the age of 35 respectively with 6.6 and 31.7% FPR. With higher DS age risk the PPV of the screen positive test was higher and the NPV of the screen negative result--lower. The percentage of invasive prenatal testing in screen positive patients was high (average 83.4%) without significant differences in the two age subgroups. Pregnancy was terminated in all cases with antenatally diagnosed DS fetuses. The ratio "lost unaffected pregnancies/1 DS fetus diagnosed antenatally" for serum screening was lower compared to the same ratio when screening by age. The results from our pilot study (serum screening sensitivity and FPR, uptake for invasive testing in screen-positive cases) are comparable to the ones reported in literature. This is an important prerequisite for introduction of mass DS screening for our population.