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A simple test to predict the sex of unborn babies at only six weeks using maternal blood could prevent the need for risky tests during pregnancy.Recently launched early gender detection tests are often viewed as an unnecessary ‘toy’ for some critics, but they could represent a substantial improvement in the rates of miscarriages or fetal injuries caused by invasive genetic testing methods.

Some congenital diseases are gender-specific, which means that affect only girls or boys. Knowing the sex of the foetus would make further tests unnecessary in about 50% of the times, but conventional methods (e.g. ultrasound) are often unable to accurately detect the gender before the week 20th, roughly half of the whole pregnancy time.

Novel DNA testing-based gender detection tests use a drop of blood safely taken from the mother’s finger to look for fetal DNA through the super-sensitive PCR technique. A lab technician can easily tell whether there is male DNA present in the sample, which indicates the the baby is a boy.

To confirm the value of this tests, The Institute of Child Health (UK) carried out a trial with about 70 pregnant women. Some were at risk of having children with X chromosome anomalies, which affect boys only. An examples is the Duchenne muscular dystrophy. Other women had risk of having a girl with congenital adrenal hyperplasia (CAH), which causes abnormal development of genitalia and, if detected early during pregnancy can be treated in the womb with steroids.
In both cases, the tests allowed the early identification of the gender, several weeks before that the ultrasound. The leader of the team highlighted the benefits of this technique in the case of women at high risks of genetic disorders: “Risks associated with invasive testing are reduced in about half of the women“.
The investigators pointed that not only invasive tests are unnecessary but also in the case of CAH, steroid administration is not required when the foetus was found to be male by seven weeks after conception.

Miscarriage riskCurrent methods to perform a prenatal genetic test require that cells from the foetus are obtained, using either amniocentesis or chorionic villus sampling (CVS). These methods use a needle that is injected into the womb. This procedure cannot be done before week 11 and can provoke a miscarriage in up to 1% of cases. Researchers have been trying to develop a non- or minimally-invasive technique for carrying out genetic tests during pregnancy. The breakthrough came when scientists found out that the mother’s blood contained tiny amounts of foetal DNA that could be detected and analyzed.

So far, the technique is used to identify genes that come from the father and are be passed on to the foetus. This includes the genes that are present on chromosome Y or the rhesus gene when the father is RH positive and the mother is negative.

Researchers are working to find more efficient ways to extract the free foetal DNA to detect single-gene alterations, such as those leading to conditions like cystic fibrosis or thalassaemia. Although the researchers involved in these developments are optimistic about the perspectives of these tests, they are also concerned about potential negative implications. They think that in some countries these tests could facilitate early abortion with gender-selection goals.Source: BBC