Cell-Free DNA Fetal Sex Tests Most Accurate After 20 Weeks

Sensitivity, specificity for detecting Y chromosome sequences highest with RTQ-PCR >20 weeks

TUESDAY, Aug. 9 (HealthDay News) -- Fetal sex determination tests using real-time quantitative polymerase chain reaction (RTQ-PCR) have the highest sensitivity and specificity for detection of Y chromosome sequences after 20 weeks' gestation, according to a meta-analysis published in the Aug. 10 issue of the Journal of the American Medical Association.

Stephanie A. Devaney, Ph.D., from the Johns Hopkins University in Washington, D.C., and colleagues reviewed available literature to examine the performance of noninvasive fetal sex determination tests using cell-free fetal DNA and to identify which variables affect performance. A total of 57 selected studies with 80 data sets, representing 3,524 male- and 3,017 female-bearing pregnancies were analyzed with covariates, including publication year, sample type, DNA amplification methodology, Y chromosome sequence, and gestational age.

The investigators found that there was significant interstudy variability, but overall performance of the test to detect Y chromosome sequences had a 95.4 percent sensitivity and 98.6 percent specificity, a diagnostic odds ratio (OR) of 885, a 98.8 percent positive predictive value, a 94.8 percent negative predictive value, and an area under curve (AUC) of 0.993. The largest effects on test performance were seen for DNA methodology and gestational age. The AUC was significantly higher for RTQ-PCR than PCR (0.996 and 0.996, respectively). For gestational age the AUC was 0.989 at <7 weeks, 0.994 at 7 to 12 weeks, 0.992 at 13 to 20 weeks, and 0.998 at >20 weeks. The comparison of diagnostic ORs across age ranges was significant. Compared to conventional PCR, RTQ-PCR showed better performance after 20 weeks compared to tests done prior to seven weeks or within 20 weeks.

"Sensitivity and specificity for detection of Y chromosome sequences was greatest using RTQ-PCR after 20 weeks' gestation," the authors write.

Two of the study authors disclosed financial ties to the biotechnology industry.

Abstract
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Physician’s Briefing Staff

Physician’s Briefing Staff

Published on August 09, 2011

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