Thursday, March 6, 2014

Antenatal Care: Diagnostic DNA Testing and other Aspects of your Prenatal Care (Guest Post)

Antenatal care (or prenatal care) is not in any way obligatory but is very important for your pregnancy. Antenatal care looks at various aspects of your pregnancy, making you undergo simple tests (or less simple antenatal DNA tests) and checkups which are aimed at one thing: ensuring the pregnancy goes as smoothly as possible and informing you of any likely complications. There is heaps of information to help you even before you begin your visits, a little breeze online and you can begin learning how your prenatal care will unfold week after week, distinguishing between your screening tests and your diagnostic tests (the latter usually involve direct fetal DNA sampling and actual analysis of your baby’s DNA)

Ultrasounds & fetal biometric measurements

Ultrasounds essentially use high frequency waves which are then turned into the imaging. Whilst X rays use radiation, ultrasounds do not and are entirely safe. The first ultrasound is usually carried out at around 20 weeks. Ultrasounds may also be performed earlier to determine whether there is a multiple pregnancy or the age of the fetus. Obstetricians can determine the position of the fetus, the sex of the baby as well as take fetal biometric measurements. These measurements ensure that the baby is the right size and that development is progressing as normal. Further diagnostic tests may then be required. These are essentially prenatal DNA tests which determine the child’s genetic health. The same procedures used to collect fetal DNA samples for a diagnostic test are also used for antenatal paternity testing/ paternity testing during pregnancy.

A Sigh of relief Mommies

So we will be looking at several tests and especially diagnostic tests and how these have certain risks; these may include injury to the baby, miscarriage or on a lighter note, some side effects such as fevers or soreness which you can easily deal with. However, within the field of antenatal tests a new science has emerged which is called “non invasive prenatal/antenatal testing”. Basically, instead of getting the sample of baby DNA from inside your womb, the sample can be collected from blood – yes, a simple blood draw from the mother will provide a sample which contains a mix of her DNA and that of her baby. The laboratory extraction process for this DNA test is more complex than that for procedures like amniocentesis and would be too much to go into for such an article. What you need to know if that whilst invasive tests carry risks, non invasive tests are absolutely “riskless” and many laboratories have focused on developing and offering these prenatal tests, including easyDNA New Zealand – see . Ask your prenatal care specialist or your doctor about these tests – given that they are relatively recent and not available in all countries, you will need to get further information and guidance.

Prenatal tests: Screening tests and diagnostic tests

Screening tests include urine testing. A urine test is used to determine your blood sugar levels as well as to check for the presence of protein which could be a sign of pre-eclampsia, a condition that most pregnant women would have heard of and that luckily, is rather uncommon. Maternal serum testing is another test carried out. Don’t be alarmed, although the term “maternal serum testing” might sound baffling and technical, all you need to know is that this is a blood test and can help determine the risk of Down’s syndrome, Edward syndrome and neural tube defects. This test measures the levels of alpha fetoprotein in the maternal blood sample. High levels of this protein may indicate anencephaly or Spina bifida (two examples of neural tube defects).
Ultrasounds are also categorized as screening tests although they sometimes are also viewed as diagnostic tests. All screening tests can provide just an indication of whether the fetus suffers from any of a range of conditions. Diagnostic tests will be able to confirm whether results of a screening test were in fact correct.

Amniocentesis, Chorionic Villus sampling (CVS) and percutaneous umbilical cord blood sampling (PUBS)

Depending on the week of pregnancy you are in, one of these three diagnostic tests will be recommended if earlier tests suggest some genetic or congenital defect. All three are invasive antenatal tests and all have certain risks. The one that is most commonly carried out is amniocentesis. This test involves withdrawing a volume of amniotic fluid from the amniotic sac. This sample of fluid is then sent to a laboratory for analysis. Laboratory analysis involves directly testing the fetal DNA in the sample to determine whether any chromosomal abnormalities are present. Amniocentesis is also used because it can reveal levels of alpha fetoprotein (something which cannot be done with chorionic villus sampling). To reiterate: high levels of alpha fetoprotein could indicate a neural tube defect such as spina bifida. The one that is least used of the three is Percutaneous umbilical cord sampling: this test is carried out at a very advanced stage of pregnancy (around 23 weeks) and the chances of miscarriage are higher than with amniocentesis and chorionic villus sampling. Remember, you do not in any way have to carry out these tests if you do not want to. However, they can help you get better prepared for the birth of a special needs child or at least, give you the option of considering whether to terminate your pregnancy or not.

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