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

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.

Korean-Specific Parameter Models for Calculating the Risk of Down Syndrome in the Second Trimester of Pregnancy

The purpose of the current study was to propose a Korean-specific parameter set for calculating the risk of Down syndrome in the second trimester of pregnancy and to determine the screening performances of triple and quadruple tests in Korean women. Using the data on triple or quadruple screening from three hospitals in Korea during 7 yr, we re-converted the concentrations of four serum markers to multiple of median values according to gestational age and maternal weight. After re-calculating the risk of Down syndrome in each pregnancy by multiplying maternal age-specific risk by the likelihood ratio values for the serum markers, screening performances and optimal cut-off values of triple and quadruple tests were analyzed. Among 16,077 pregnancies, 23 cases had Down syndrome (1.4/1,000 deliveries). Compared to the previous program, the tests with new parameters had improved screening performance. The triple and quadruple tests had detection rates of 65.2% and 72.7%, respectively, at a false-positive rate of 5%. The optimal cut-off value for the quadruple and triple tests was 1:250. We have presented a Korean-specific parameter set for Down syndrome screening. The proposed screening test using this parameter set may improve the performance of Down syndrome screening for Korean women.

Interpretation of antenatal screening methods / 대한산부인과학회지

For definitive antenatal diagnosis of fetal aneuploidy, invasive tests such as chorionic villous sampling, amniocentesis and cordocentesis are required for chromosome analysis. However, to reduce the risk of miscarriage associated with procedural complications, it is important to detect pregnant women with high risk of fetal aneuploidy. Recently, there have been advances in maternal serum and sonographic markers for screening of chromosomal defects in the first and second trimester. The serum screening methods include first trimester screening with nuchal translucency and second trimester multi marker screening. Particularly, combining first and second trimester results can increase the detection rate of Down syndrome with lower false-positive rates. In addition to biochemical markers, second trimester sonogram to detect major and minor sonographic markers for chromosomal defects is important to identify the high risk pregnancy. To detect the fetal aneuploidy with high specificity and sensitivity, we need to interpret the maternal age, the results of first and second trimester serum markers and genetic sonographic findings all together.