New blood test can detect fetus gender in early pregnancy

A boy or a girl baby. Parents-to-be wishing to know the gender of their unborn baby can usually find out during a routine ultrasound performed around 20 weeks of pregnancy. Now, new technology can tell pregnant women whether they are having a boy or a girl as early as seven weeks into a pregnancy. Scientists have been making rapid progress in identifying foetal DNA in the mother’s blood to predict fetus gender.

As a noninvasive method of determining the sex of a fetus, tests using cell-free fetal DNA obtained from the mother’s blood after 7 weeks gestation performed well, while urine-based tests appear to be unreliable, revealed by researchers recently in a new study in JAMA.

“The availability of a reliable noninvasive alternative to determine fetal sex would reduce unintended fetal losses and would presumably be welcomed by pregnant women carrying fetuses at risk for disorders,” the authors write.

Using cell-free fetal DNA as a noninvasive method for prenatal determination of fetal sex provides an alternative to invasive techniques for some heritable disorders.

Stephanie A. Devaney, Ph.D., of the National Institutes of Health, Bethesda, Md., and colleagues performed a systematic review and meta-analysis of previous research to examine the analytic validity of cell-free fetal DNA testing, which describes the test’s ability to detect Y chromosome sequences within maternal samples, as well as the clinical validity of the test, as indicated by its ability to correctly identify fetal sex.

The researchers found that the overall performance of the tests had sensitivity of 95.4 percent, specificity of 98.6 percent, positive predictive value, 98.8 percent, and negative predictive value, 94.8 percent.

Performance was high using maternal blood.

DNA methodology and gestational age had the largest effects on test performance, with real-time quantitative polymerase chain reaction (RTQ-PCR) outperforming conventional PCR.

Test performance was high if performed using RTQ-PCR on a blood sample taken at a time during pregnancy when sufficient cell-free fetal DNA was present (7 weeks’ gestation or later), with the best performance after 20 weeks’ gestation.

Testing performed prior to 7 weeks’ gestation using blood, and all tests using urine, were found unreliable.

Source: Journal of the American Medical Association, USA



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