Fetal DNA in Maternal Blood and Prenatal Paternity Testing

Scientists have managed to sequence fetal DNA in maternal blood. Prenatal paternity testing  is used to establish paternity of an unborn child during pregnancy. Non invasive testing is a 0% risk test which is being used successfully to determine paternity. It is also likely that in future, non invasive fetal DNA sampling will be used to determine any hereditary illnesses or chromosomal abnormalities. Prenatal DNA testing involves analysis of fetal DNA in maternal blood. But how does your baby’s DNA make its way into your blood stream? The answer is through the placenta.

Functions of the Placenta

Your placenta is the interface between your blood supply and that of your unborn baby. Its function is to provide your baby with oxygenated blood as well as important mineral and nutrients. In addition to providing oxygen and nutrition, your placenta also filters out deoxygenated blood and waste products. These waste products form a large part of the amniotic fluid, or your ‘waters’. Babies do not urinate before birth and not before the end of the first trimester. Unlike the urine we produce, a baby’s urine contains no urea.  Later in the pregnancy, fetal urine becomes an essential component of amniotic fluid (the fluid extracted during amniocentesis).

Any fluids found in the womb contain fetal DNA. That fetal DNA passes into the maternal bloodstream via the placenta, and can be used to establish whether or not a specific guy is the father of your baby. Prenatal paternity testing can confirm the paternity of a child your child DNA by comparing the DNA derived from the fetus to that of the alleged fathers.

How is the non invasive prenatal test carried out?

First and foremost we need to establish something very important: You should not do a prenatal paternity test of this type unless you are a minimum of 10 weeks pregnant- 10 weeks must have elapsed from the first day of your last period. If you do the test earlier, paternity might not be established.

The test requires blood samples- this is the main advantage over invasive methods of DNA sampling and makes non invasive testing 100% risk free. Normally the laboratory or company doing your DNA test will provide you with a kit. You go to a nurse or doctor and take your kit with you for sample collection. Inside the kit there are blood collection tubes which the person taking blood samples will need to fill. This test is done with a standard blood draw from the median cubital vein that runs along the inside of your arm- there is nothing to worry about.

Blood samples need to then be sent promptly to the lab- this is very important as blood samples need to be tested shortly after they have been collected. Over 300,000 genetic markers are compared using a combination of genetics and computer science known as ‘advanced bioformatics’ –The results will be no less accurate than 99.9% – this is the minimum standard needed to ascertain paternity.

Non Invasive prenatal paternity Tests are of 2 types

Scientists can carry out a prenatal paternity test by either analyzing cell free fetal DNA or nucleated fetal DNA. Cell free DNA means that DNA strands and fragments are not enclosed within a cell whilst nucleated DNA refers to DNA that is enclosed with the cell nucleus which is in turn enclosed in the actually cell.

Prenatal tests for paternity that use cell free fetal DNA and not cellular DNA are more reliable. This is because cell-free fetal DNA is constantly filtered out of the body, leaving the mother’s body via her urine. Nucleated fetal cells sometimes persist for a few weeks in the maternal blood stream. This means that an expectant mother could carry nucleated fetal DNA from her current pregnancy as well as nucleated fetal cells from her previous pregnancy. This may cause a misdiagnosis because scientists will be unable to tell whether they are analyzing fetal DNA from the current fetus or fetal DNA from the previous pregnancy.

The Alleged Father Must Agree

For a Prenatal paternity test blood samples are required from the alleged father and the mother. The kit will contain the required blood collection tubes as well as a consent form which all people giving samples will have to sign. Non invasive prenatal paternity testing can only be done with blood samples. If the alleged father is not available for the test or willing to do prenatal paternity test you may have to consider other options (perhaps waiting till after the birth of the child or pursue a legal course of action)

For non invasive testing you will be required to supply a sample of your blood and a sample of the alleged father’s blood. This test only uses the baby’s DNA in your blood to compare with that found in the alleged father’s DNA profile taken from his blood.

A word about Baby Gender Prediction Testing

The fact that fetal DNA is found in the maternal blood stream means that it is also found in the maternal urine. The fetal DNA in maternal urine is very little and cannot be used for a prenatal paternity test as the amount of DNA is too small as well as too fragmented. But, what can be done with maternal urine, is a gender prediction test. Scientists can know the sex of your baby by locating the genetic markers in urine and depending on whether they are male of female genetic markers they can know the gender of your child.