It is not uncommon to carry out prenatal DNA testing to find out whether an unborn fetus is a carrier of any hereditary illnesses. Women who fall pregnant after the age of 35 or around that age are often encouraged to carry out diagnostic tests such as amniocentesis or chorionic villus sampling to ensure the fetus is developing healthily.
Usually diagnostic tests follow screening tests when the latter indicate the possibility of the baby suffering from conditions such as Down’s syndrome. Screening tests can only provide indications and cannot confirm defects with absolute certainity. The incidence rate for Down’s syndrome children is known to be considerably higher in women who fall pregnant in their 30s.
It is important to know whether the unborn baby is developing healthily even if a termination of pregnancy is out of the question. If you know that you will have a handicapped baby you may want to prepare differently, read up on antenatal care, get in touch with support groups or seek antenatal advice.
Screening tests and Diagnostic Prenatal Tests
Screening tests are non-invasive. Ultrasonography is the most well known and commonly used of screening tests (although it can also be considered a diagnostic test as it can sometimes confirm genetic abnormalities in an unborn child). Such tests may provide an indication that the unborn baby has a condition such as Down’s syndrome or neural tube defects. For example, certain folds and creases in the neck (nuchal folds or nuchal translucency) would indicate the unborn baby is suffering from Down’s syndrome. However, a screening test cannot confirm whether the baby has the condition. In fact, screening tests might give you false positive results. A diagnostic test such as amniocentesis or chorionic villus sampling will give a definite answer. Diagnostic tests allow scientists to get a sample of the fetus’s DNA which they can then analyze to confirm whether the child has the chromosomal abnormality that causes Down’s syndrome.
The only problem with amniocenteses or chorionic villus sampling is the incidence of miscarriage following the procedure. Although the incidence is minute, it is still a very serious issue. Estimates vary but all estimates provide figures which are very low. According to the American College of Obstetricians and Gynecologists (ACOG), the loss rate from the procedure is as low as 1 in 300 to 500
Fetal DNA sequencing from maternal blood
Scientific studies have shown increased levels of fetal DNA in the maternal blood stream as pregnancy progresses. This discovery has changed the way we think of prenatal testing and has enabled a risk free method for non invasive prenatal diagnosis. Scientists have located a vein that is particularly rich in fetal DNA and more importantly they have overcome the challenge of separating fetal DNA from maternal DNA. Cell free fetal DNA in the mother’s blood can only be analyzed using very advanced techniques making the test very expensive. Fetal DNA sequencing for hereditary illnesses is extremely complex and involves analysis of hundreds of thousands of single nucleotide polymorphisms (SNPs). They can even determine from which parent the illness was passed to the child.
Fetal DNA found in the maternal blood group is already being used for prenatal paternity testing with success.
Findings about Fetal DNA:
The following are some findings about fetal DNA in maternal blood:
Fetal DNA sequencing from maternal blood offers a 100% risk free way of prenatal diagnosis.
- Certain fetal abnormalities such as Trisonomy 21 can cause changes in the levels of fetal DNA in the maternal blood stream. Visit this page for more information.
- The quantities of fetal DNA increase considerably as pregnancy progresses. Levels of fetal DNA might be negatively affected if certain fetal abnormalities such as Trisonomy 21 are present.
- Fetal DNA sequencing for autoimmune illnesses may eventually be used as diagnostic tests, possibly replacing procedures such as amniocentesis or chorionic villus sampling.
Once complication of the fetal DNA sequencing for autoimmune disorders/ hereditary illnesses is the difficulty of distinguishing female fetal genetic markers which genetic markers belonging to the mother.
There is still much research to be done in the field but the future for fetal DNA sequencing for illnesses is looking indeed good. Prenatal DNA testing in a way that is non invasive is changing the way we look at such tests.