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WHAT IS PRENATAL SCREENING?
The majority of babies conceived are healthy, however problems can occur due to a number of different factors, such as the age of the parents and genes.
One of the main concerns of a pregnancy is the risk of Down syndrome, which is an uncommon chromosomal issue. Down syndrome involves the fetus having an extra chromosome 21 and therefore being born with physical and intellectual disabilities.
There are a number of screening tests that can confirm if your baby does or does not have any particular conditions. The tests can give an estimate of the likelihood of any problem being present during your pregnancy. The risk is generally said to be ‘high’ or ‘low’, instead of a definitive yes or no. The tests that can give a ‘yes’ or ‘no’ answer is called diagnostic tests.
WHAT TYPES OF PRENATAL SCREENING ARE THERE?
There are several different types of prenatal screening tests that are available, including:
- First trimester screening
- Non-invasive prenatal screening (NIPS)
- Diagnostic tests
- Mid-trimester ultrasound
- Genetic testing
The first trimester combined screening tests for Down Syndrome. The test is based on maternal age, the hormone level from maternal blood are taken at roughly 10 weeks gestation, and an ultrasound used to measure the neck skin thickness (nuchal translucency) at 12-13 weeks. The result that is received allows us to estimate the risk of the baby having a chromosomal abnormality of chromosome 13, 18, or 21 (Down syndrome).
The parent can choose to obtain foetal DNA to confirm any problems if the result indicates a high risk. This can be achieved by either amniocentesis or chorionic villus sampling (CVS) (placental sampling at 12-13 weeks). Your obstetrician can help to explain the significance of the results.
Some people choose not to have screening for Down syndrome as they do not wish to risk a pregnancy with an invasive test, nor do they wish to terminate the pregnancy even if the risk is high.
NON-INVASIVE PRENATAL SCREENING (NIPS)
There have been significant recent advances in the way foetal DNA is obtained. Now it is possible to take blood from a pregnant mother any time after 10 weeks gestation, and obtain small fragments of fetal DNA that are floating in her bloodstream. These fragments of DNA can be tested for a large number of abnormalities, as well as a number of less common syndromes.
The test has been named NIPS (non-invasive prenatal screening) and the DNA results are overwhelmingly more reliable than other tests done during the first trimester. NIPS has reduced the number of women that require amniocentesis and CVS.
A number of women choose to have this test first instead of undergoing the more traditional first trimester combined screen. It is recommended that women who choose to have NIPS also have a 12-week ultrasound to pick up any anatomical problems that are not tested for using NIPS.
Women over the age of 40 or those with a high risk for other reasons may be recommended NIPS.
Your obstetrician will help you decide what type of screening is best for you.
Diagnostic tests are able to give a definitive answer regarding whether your baby has any particular health issues. The diagnostic tests are amniocentesis or CVS.
These tests take a sample from the fluid around the baby or from the placenta to check the chromosomes of the baby. They can almost always provide a definite answer regarding the baby’s chromosomes.
Diagnostic tests require a needle to be inserted into the uterus, and do carry a one per cent or less chance of losing the pregnancy. You will be provided with all the relevant information regarding the benefits and risks before you decide on what test you want to have.
This ultrasound allows a specialist to carefully check that your baby’s structure and organ development is normal. Most problems that are detected are minor, and if further advice or assessment is needed your obstetrician will give your guidance.
Mid-trimester ultrasounds are also able to check for any other forms of abnormalities that may have occurred in the placenta or cervix and confirm a due date.
Some genetic tests can be performed before pregnancy occurs to see if either parent is a carrier of any conditions. These include a new reproductive genetic carrier testing that can test for carrier status of three common inherited conditions:
- Fragile X syndrome (FXS)
- Spinal muscular atrophy (SMA)
- Cystic fibrosis (CF)
It is important to discuss with your partner what your attitude is towards screening and invasive testing, preferably before conception. Screening tests are simply an indication of a condition that is present and at least one of the invasive tests are often needed to confirm. These tests carry a slight chance of miscarriage.
If you decide to go down the path of screening, you should be prepared to undergo at least one form of invasive testing to gather accurate information.
Talk to your doctor about your options.
If you have any further queries, our friendly team at My Obg will be happy to assist you. Call us on (03) 9731 1006 or email us at firstname.lastname@example.org