It is compulsory that pregnant women of all ages undergo screening and invasive diagnostic testing for chromosomal abnormalities before they are up to 20 weeks’. Of course, recent developments in screening methods have widened the options for patients.
Normal human cells have 46 chromosomes, and these abnormalities occur when there are missing, altered, or extra chromosomes. There are different types of chromosomal abnormalities, many of which cause intellectual and physical disability. Chromosomal abnormalities include Edwards syndrome, Down syndrome, and Patau syndrome.
Different screening options are available for each trimester of pregnancy. Screening options in the first trimester include nuchal translucency testing together with the measurement of pregnancy-associated plasma protein A and human chorionic gonadotropin.
Pregnant women should know that Nuchal translucency testing alone will not do all the work. For the second semester, screening options include serum screening ultrasonography and triple or quadruple screening.
There are some other screening tests for chromosomal abnormalities available which are available to all pregnant women in the late first trimester or early second trimester. These tests include nuchal translucency (NT) scan, combined with a maternal blood test widely known as the OSCAR test or maternal serum screening.
Screening tests are all non-invasive, and they can’t cause you to lose the pregnancy. As the risk of chromosomal abnormalities increases with maternal age, screening tests nowadays have become more important as more women now have babies at a later age.
Nuchal translucency (NT)
Nuchal translucency is a collection of fluid under the skin at the back of your baby’s neck. The amount of fluid is measured during a nuchal translucency (NT) ultrasound scan. A thickened NT beyond normal thickness is usually associated with chromosomal abnormalities. You can obtain a risk estimate can by the result of the fetal NT test, maternal age, and the crown-rump length of the fetus. Please note that the accuracy of the NT test alone is just about 80%.
According to a research, the test involves the NT test in addition to a sample of the mother’s blood which is analyzed for levels of free beta hCG and Pregnancy-associated plasma protein A. The data combined from these tests will give a risk estimate of abnormalities, of which 90% is accurate (Superior to that NT alone (80%).)
Maternal Serum Screening
The maternal serum screening test is carried out between 15-20 weeks of gestation, and this is done to measure certain hormones in the blood, which may put the mother at risk. The triple test analyses three hormones called alpha-fetoprotein, human chorionic, oestriol, gonadotropin, and a risk value is determined according to the gestational and maternal fetus’s age at that time. As its accuracy is just 65%, this test is not done as much as before. Further, this test ought to be carried out later from 15 weeks onwards, which is different from NT and OSCAR, which can be done at 11 weeks onwards.
Non-Invasive Prenatal Test (NIPT)
In 1997, scientists first reported the presence of small amounts of baby’s DNA (known as cell-free DNA, or cfDNA) in the mother’s blood as early as four gestational weeks1 . The rapid development of next-generation sequencing technology makes it possible to detect the risk of having chromosomal abnormalities including Down Syndrome, Patau Syndrome, Edwards Syndrome and other genetic conditions non-invasively.
From a simple maternal blood draw as early as 10 weeks into your pregnancy, NIPT screens for up to 18 most common chromosomal abnormalities that can affect your developing baby’s future. This test is done with little or no risk to your pregnancy. The accuracy rate of this test is up to 99%.