Objective. To evaluate sensitivity, specificity, positive and negative predictive values, likelihood ratios, post-test probabilities and other indicators of reliability of the combined test in prenatal diagnostics.
Methods. This study was a retrospective analysis of the data of pregnant women who were consulted during 2005-2010 in the Centre for Medical Genetics. The combined test was performed at 11-13 weeks + 6 days of gestation. Outcomes of all pregnancies were known from questionnaires or obtaining information on the condition of their newborns by telephone. The indicators of reliability of the combined test were evaluated.
Results. 833 women were included into the study. Combined test was positive in 90 (11.3%) pregnant women. 163 (18.3%) women underwent amniocentesis test and in 14 (1.7%) cases the result showed a pathological kariotype. In this study the combined test sensitivity and specificity were 84.6% and 94.6% respectively. Pre-test probability that pregnant women carry a fetus with chromosomal abnormality was 1:250 or 0.004. Post-test odds after the combined test to detect this abnormality were 0.06. The post-test probability of the same disease was 5.92% when the the combined test was positive. When combined test was negative, posttest odds were 0.0006 and post-test probability was only 0.06%.
Conclusions. The combined test used as a screening test is a valuable method in prenatal diagnostics as it correctly identifies prenatal pathology in most of the cases and is a reliable means in reassuring that a fetus is healthy. The combined test, if used methodologically correctly, has a high predictive value in detecting fetal chromosomal abnormalities.
Keywords: combined test, chromosomal abnormalities, nuchal translucency, free P-hCG, PAPP-A, amniocentesis.
