Fetal DNA In Maternal Blood Provides Accurate Sex Prediction

Free-floating fetal DNA in a mother’s blood can accurately predict fetal sex. When using real-time quantitative (RTQ)-polymerase chain reaction (PCR) to amplify fetal DNA, a simple, noninvasive blood test could provide a viable alternative to invasive cytogenetic determination, according to researchers who conducted a systematic review and meta-analysis on the topic (Devaney SA, et al. JAMA. 2011; 306:627-636).

The test, which detects Y chromosome DNA sequences in the maternal blood, showed a sensitivity (proportion of male fetuses with a positive test result) of 95.4% and specificity (proportion of female fetuses with a negative test result) of 98.6% from 80 data sets derived from 57 studies. It showed a positive predictive value of 98.8% and a negative predictive value of 94.8%.

DNA testing technique and gestational age had the greatest effect on the test’s performance; tests using urine proved unreliable, as did tests done before 7 weeks of gestation. Testing after 20 weeks provided the greatest reliability. In addition, RTQ-PCR outperformed standard PCR in sensitivity and specificity.

A disadvantage the researchers cited is the test’s inability to validate female sex, because the test only checks for male chromosomes. “Other potential disadvantages include that DNA testing is not available at point of care, not presently approved by the Clinical Laboratory Improvement Amendments, and not currently reimbursed by insurers,” they wrote.