Sensitivity and specificity of prenatal screening methods for detection of risk of fetal chromosomal abnormalities

ABSTRACT

Background: Babies born with chromosomal abnormalities pose a burden on the family as well as the society at large. Early detection and management of fetal chromosomal abnormalities has become an essential component of antenatal care. Hence pregnant women of all ages are offered screening methods for early detection of chromosomal abnormalities. We intended to study the sensitivity and specificity of prenatal screening methods for detection of risk of fetal chromosomal abnormalities.Methods: A three-year retrospective study was conducted from January 2015 to December 2017 in 258 singleton pregnant mothers attending antenatal clinic and delivering at DMCH. The patients were screened for chromosomal abnormalities in the first trimester by NB NT scan along with dual marker and level II anomaly screen scan along with quadruple test in the second trimester. Based on the test results the patients were classified into high risk and low risk pregnant mothers. All the patients with abnormal quadruple test were subjected to amniocentesis for karyotyping. The results of the first trimester and second trimester screening methods were statistically analyzed using chi square test, sensitivity and specificity of the prenatal screening methods was calculated.Results: The sensitivity and specificity of dual marker test for detection of chromosomal abnormality is 50% and 85.94% respectively and that of quadruple test sensitivity is 50%, specificity is 95.3%. The difference was highly significant in the favour of the quadruple marker with P-value of 0.0004.Conclusions: While counseling the patients regarding possibility of having abnormal fetus, obstetrician should keep in mind the false negatives and false positives of prenatal screening and diagnostic methods.