Prenatal diagnosis of chromosomal abnormalities

Abstract

INTRODUCTION: Chromosomal abnormalities are alterations in sex or autosomes chromosomes, they
can be structural or numerical. Down syndrome or trisomy 21 is one of the most frequent chromosomal
abnormalities, where 95% of the conditions are due to a complete trisomy. These alterations produces a
significant increase in morbidity and mortality, it is important to know risk factors and suspect them prenatally. The most used methods for prenatal screening of these abnormalities are serological markers
and ultrasound imaging tests. The detection of fetal DNA that circulates freely in maternal plasma is an
other non-invasive prenatal diagnostic tests that can be used.
METHODOLOGY: A structured clinical question was raised from a clinical setting. A bibliographic search
was conducted in Pubmed in order to finding an article that could answer our structured question about if
the study of circulating fetal DNA compared to combined screening is a more sensitive and specific
diagnostic method to detect Down syndrome. The article whose title is: "Cell-free DNA Analysis for
Noninvasive Examination of Trisomy", was selected.Analysis of the article: In order to answer our
structured clinical question, a secondary analysis was performed to calculate sensitivity (S), specificity (E),
positive predictive value (VPP), negative predictive value ( NPV) and its respective 95% confidence
interval (95% CI). We also highlight the result of the area under the curve (ABC) of the ROC (Receiver
Operating Characteristic) curve.
CONCLUSION: fetal DNA screening has higher sensitivity and specificity compared to combined
screening (ultrasound and biochemical tests) for the diagnosis of Down syndrome. But its high cost still
implies a limitation to solve.