The Science behind our Non-invasive Prenatal Paternity Test
Our non-invasive prenatal paternity test can accurately confirm the paternity of an unborn child as early as the 10th week of pregnancy using a maternal blood sample. This is possible because scientists have succeeding in detecting cell-free fetal DNA circulating in the mother’s blood stream and using this DNA to map the unborn child’s genetic markers.
As pregnancy progresses the amount of fetal DNA in the maternal blood stream increases. Fetal DNA is present even in the early stages of pregnancy but quantities are too small for any meaningful analysis to be made.
DNA Analysis in Non-invasive Prenatal Testing
The DNA we analyze is cell-free DNA – in other words the DNA is not enclosed in a cell as is normally the case with our DNA. Cell free DNA constantly enters the mother’s blood stream throughout pregnancy.
Our non invasive prenatal paternity test Our non invasive test using cell free fetal DNA offers a true advantage over non invasive tests that look at whole fetal cells in maternal blood, in that the chances of misdiagnosis due to any previous pregnancies are not present.
Other non invasive tests use fetal DNA enclosed in cells (nucleated fetal DNA); this can persist in the maternal blood stream for years after a pregnancy and therefore, a pregnant mother could carry fetal DNA from a previous pregnancy in her blood stream. This means that there is the possibility of misdiagnosis if any DNA from previous pregnancies remains in the maternal blood stream. Interpretation of results can also be difficult with prenatal testing that uses whole/ nucleated fetal cells.
How does Baby DNA enter the Mother’s Blood stream?
A baby’s DNA enters the mother’s blood stream via the placental wall (the placenta is where nutrients, waste and oxygen are exchanged between mother and baby). Once scientists have the maternal blood sample, they separate the maternal plasma from the rest of the blood. Cell free fetal DNA and maternal DNA are found in the blood plasma (plasma being one component of blood). Because cell-free fetal DNA is often fragmented, scientists use a technique to detect Single Nucleotide Polymorphisms (SNPs) to analyze the fetal DNA fragments; other DNA testing techniques used in many standard DNA tests (such as Short Tandem Repeat or STR analysis) are ineffective with cell free fetal DNA because STR analysis requires DNA to be intact.
Typically, the amount of fetal DNA in a maternal blood sample taken after the 12th week of pregnancy is around 15% (see our Frequent Questions about Non-Invasive Prenatal Paternity Test to understand how to calculate time of conception).
Why is our Test so Accurate?
The accuracy of our test is based on the fact that we analyze over 300,000 genetic markers using what are known as advanced bioformatics (bioformatics is the application of IT and computer science to the field of genetics). Bioformatics are used to precisely compare the genetic blue prints of the alleged father and child to confirm or rule out paternity. If the probability that the alleged father contains the genetic markers required of the biological father is greater than 99.9% when compared with random individuals, paternity is concluded. If the alleged father matches no better than an unrelated individual, he can be excluded as the biological father. Our test is therefore extremely conclusive.
Note: The prenatal paternity test can give an inconclusive result if the alleged fathers are close relatives (for example, brothers) or from the same small ethnic minority. In such situations, it is important that we test both alleged fathers.
Ordering your Prenatal Paternity Test in New Zealand
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