Science behind the Test

How does a Gender Test work?

The science behind KnowtheGender test relies on analyzing the traces of fetal DNA in the mother’s urine. Dead fetal DNA finds its way through the placental wall into the mother’s blood stream. The fetal DNA gets filtered out through the kidneys, passing out with the mother’s urine. Significantly, it is actually cell-free DNA that is found and very often, this DNA is just in fragments. However, the fetal DNA found enables us to conclusively tell you the sex of the child you are expecting.

A human male cell contains 23 pairs of XY chromosomes. The Y chromosome is specific to males, encoding the characteristic of maleness. A female cell contains 23 pairs of XX chromosomes.

In KnowtheGender’s gender prediction test, scientists look for the presence of the Y chromosome or Y-specific genetic markers in the maternal urine sample provided. The Y chromosome is specific to males and if its presence is confirmed in the maternal urine, then the mother is expecting a baby boy.

If no Y chromosome is detected in urine sample, then the mother is expecting a baby girl.

The above clearly explains why it is so important to avoid any contamination of the urine sample with male DNA. If the urine sample is contaminated with foreign male DNA, scientists will detect the presence of the Y chromosome in the maternal urine and wrongly attribute this to the gender of the unborn child.

Scientific Resources on Gender Testing

1. PCR detection of cell-free circulating fetal DNA in maternal plasma and serum (Lo et al. Lancet 1997; 350:485-7)
2. Earliest detection of fetal DNA: 5 weeks of gestation (Prenatal Diagnosis, 2003; 23: 1042)
3. Source of fetal DNA? Passive diffusion across placental barrier (van Wijk et al. Clinical Chemistry, 2000; 46:729-731)