I am sure all parents are wondering what is their baby doing inside the belly and how healthy is their baby? There are few ways we can answer this question.
First trimester screening (FTS) is usually the first screening test that is offered by your obstetrician when you enter your first trimester of pregnancy. The best window of doing this test is between 11 weeks to 13 weeks +6 days of your pregnancy, or when the fetus’s crown-lump length (CRL) is 45mm -84mm. FTS is suitable for all ages but it is not a compulsory test to do. If you are above 35 years old with a family history of having syndromic babies, you fall in the high risk category. For parents who would like to know more about their babies’ health, they are encouraged to go for the test.
What is a screening test?
It is very important to remember what a screening test is before getting one performed. This will help alleviate some of the anxiety that can accompany test results. Screening tests do not look only at results from the blood test. They compare a number of different factors (including age, ethnicity, results from blood tests, etc…) and then estimate what a person’s chances are of having an abnormality is.
These tests DO NOT diagnose a problem; they only signal further testing should be done.
The test is necessary for you to know what is your chance of having a Down’s Syndrome (Trisomy 21) baby - who usually have mental retardation when they are born. We call it Trisomy 21 because they have an extra copy of chromosome number 21 making up to a total of 47 chromosomes while a normal human will have a total of 46 chromosomes instead. Besides Down’s Syndrome, this test also reveal the risk for less common trisomies which are Patau (Trisomy 13) and Edwars’s Sydrome (Trisomy 18). Patau and Edwards syndrome are more severe conditions and usually they are not compatible with life.
During the day of scanning, a sonographer will do a measurement of the fluid collection between the neck and the skin of the baby and we call it Nuchal Translucency. At the same time, the presence or absence of nasal bone will be assessed too. A blood sample is then drawn from the mother to check if the protein (free beta HcG and PAPPA) level is normal in the mother’s blood. The result will be obtained usually within 2 weeks. A normal measurement of Nuchal Translucency should be below 3mm and if the nasal bone is present you have 75% chance of carrying a normal baby while a combination test of scanning and blood test (FTS) will give you 95% of reassurance with a false positive rate of 5%. This means that :
Approximately 95 out of every 100 babies affected by the abnormalities addressed by the screen will be identified.
Approximately 5% of all normal pregnancies will receive a positive result or an abnormal level.
A positive test means you have a 1/100 to 1/300 chance of experiencing one of the abnormalities.
It is important to realize a positive result does not equate having an abnormality, but rather serves as a prompt to discuss further testing while a negative result also doesn’t mean that your baby is 100% free from having an abnormality. A screening test cannot guarantee the outcome; in fact, we are giving you a likelihood of your baby inheriting a genetic disease. A further diagnostic test such as CVS (chorionvillus sampling) or amniocentesis should be discussed with your doctor if a positive result is obtained.
What are the reasons for further testing?
The First Trimester Screen is a routine screening that is not an invasive procedure. The reasons to pursue further testing vary from person to person.
Performing further testing allows you to confirm a diagnosis and then provides you with certain opportunities, such as:
Begin planning for a child with special needs
Start addressing anticipated lifestyle changes
Identify support groups and resources
Make a decision about carrying the child to term
Some individuals or couples may elect not to pursue testing or additional testing for various reasons:
They are comfortable with the results no matter what the outcome
Because of personal, moral, or religious reasons, making a decision about carrying the child to term is not an option
Some parents choose not to allow any testing that poses any risk of harming the developing baby
It is important to discuss the risks and benefits of testing thoroughly with your healthcare provider. Your healthcare provider will help you evaluate if the benefits from the results could outweigh any risks from the procedure.
What are the risks and side effects to the mother or baby?
Except for the discomfort of drawing blood, there are no known risks or side effects associated with the First Trimester screen. There is a 5% false positive rate for the test. Parents should be aware of the possibility of receiving abnormal results and then finding, after further testing, the baby is normal.