Non-invasive prenatal determination of fetal sex using cell-free fetal DNA provides an alternative to invasive techniques for some heritable disorders. New research revealed that widely available blood tests that predict gender are extremely accurate. Furthermore, the tests work more than seven months before the baby is born. The Tufts University study was published in the “Journal of the American Medical Association”.

From 57 selected studies, 80 data sets (representing 3524 male-bearing pregnancies and 3017 female-bearing pregnancies) were analyzed.  The researchers used a real-time quantitative PCR to detect Y chromosome sequences in the maternal bloodstream. 

The study found that the test was 95% accurate in women who were at least 7 weeks pregnant. Amniocentesis and ultrasounds, traditional tests used to determine a baby's gender, are accurate only later, researchers said. Also, sensitivity and specificity for detection of Y chromosome sequences was 99% after 20 weeks' gestation.

The researchers also said the blood test may be a breakthrough for women at risk of having babies with sex-linked hereditary diseases. These women can now avoid invasive procedures used to determine gender in early pregnancy.