The Diagnostic Value of Combined Test for Trisomy 21 and 18 Screening in Over 35-Years Old Pregnant Women in the Gestational Age of 9-14 Weeks



Shahshahan Z¹ ; Azami N² Show Affiliations
Source: Journal of Isfahan Medical School Published:2013

Abstract

Background: Early diagnosis of congenital anomalies and termination at early pregnancy can prevent the birth of these children. The Step-wise sequential test has the most sensitivity in this regard; but because of the religious and legal rules in our country (the abortion must be done before 17 weeks of gestation or 19 weeks of LMP), it is better to use a test that is performed in first trimester and has high sensitivity rate; so the use of invasive procedures become less. We aimed to estimate the diagnosis value of combined test (free beta-hCG, nuchal translucency, and pregnancy-associated protein A) for trisomy 21 and 18 screening. Methods: In this cross sectional study, 380 pregnant women with the age of more than 35 years referred to Beheshti and Alzahra clinics (Isfahan, Iran) at the 9-14 weeks of gestation were enrolled. Combines test analysis was done with Alpha software and the sample population was divided to highand low-risk portions for trisomy 21 and 18. The high risks went on amniocentesis and the other group followed after birth for detecting if there were any signs of syndromes manifestation. Findings: For trisomy 21 (Down's syndrome), the sensitivity of combined test was 100%, and the specificity was 96.4%, with a false positive rate of 3.5%. For trisomy 18, it was 75% for the sensitivity and 100% for the specificity, with a false positive rate of 0%. Conclusion: Regarding to high sensitivity and specificity of the combined test in our population compared to other societies, we can use this test with more confidence. So, diagnosing the maternal anomalies in early first trimester could be done and we could terminate pregnancies with proven trisomy 21 and 18 legally.