Cell free fetal DNA blood test predicts sex

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) If parents-to-be are interested in very early prenatal sex determination, a new blood test is available. Now, curious parents can choose a pink or blue nursery very early.

A recent study review finds that a noninvasive method of determining fetal sex after 7 weeks gestational age is quite accurate and more reliable than tests using mother's urine samples.

"If you want  to determine your baby's sex, take a blood test."

The authors report that a noninvasive alternative that can reliably determine fetal sex may reduce unintended fetal losses caused by the more invasive tests that are currently in place.

The gold standard protocol for determining fetal sex and single-gene disorders is cytogenetic determination, but this test is invasive and possibly dangerous to the fetus. With amniocentesis, there is a small risk of miscarriage.

The third option is sonography, but this can only be performed at 11 weeks and isn't as reliable as the cell-free DNA test available after 7 weeks gestational age.

The researchers suggest a medical application for this simple to perform blood test: Parents whose fetuses at risk for gender-linked physical disorders could discover the baby's sex in a timely manner.

This cell-free fetal DNA method to determine prenatal fetal sex does provide a nice alternative to those parents whose children may inherit disorders too. Several European countries use this test routinely. Researchers also report that companies are offering this technology directly to patients over the Internet. It is marketed only as a curiosity test online and advertises a 95 to 99 percent accuracy rate as early as 5 weeks' gestational age.

Stephanie A. Devaney, Ph.D., of the National Institutes of Health, Bethesda, MD., and colleagues performed a review of previous research to determine the validity of cell-free fetal DNA testing. This test detects Y chromosome sequences (the genetic determinant of male sex) in maternal blood samples.

The researchers also reviewed and determined the clinical validity of the test in each study. The researchers chose to review 57 studies that included over 6,500 pregnancies.

Overall, the researchers found that the tests accurately determined the sex of the fetus greater than 95% of the time over several measures of statisticaly measurement . As the pregnancy moved forward over weeks, the tests became more accurate, with best performance after 20 weeks gestation. Any testing before seven weeks was determined to be unreliable.

This review and analysis of previous studies is published in the August 10 2011 issue of The Journal of the American Medical Association.

Reviewed by: 
Review Date: 
August 10, 2011
Last Updated:
August 14, 2011