Let’s Delve Deeper into the Diagnosis of Down’s Syndrome
If you are pregnant, your doctor would have discussed your families’ medical history by now. One major reason for this is that doctors want to determine whether your baby has any chance of suffering from chromosomal abnormalities. There are different kinds of these abnormalities and one of them is the Down’s syndrome. In this post, we will give a brief glimpse about its history and diagnosis.
The story about this syndrome dates back to 1866 when John Langdon Down found children suffering from mental retardation. He named them “Mangoloids” as they resembled the people of Mongolia. Owing to the ethnic insult this name caused, this medical condition was renamed as the Down’s syndrome. In 1959, Jerome Lejeune and Patricia Jacobs independently discovered that it was caused due to trisomy or triplication of the 21st chromosome.
Diagnosis of Down’s syndrome:
This syndrome can be detected during pregnancy or after the birth of the child. However, the American Congress of Obstetricians and Gynecologists (ACOG) recommend that every woman should undergo a Down’s syndrome screening test.
The diagnosis of this syndrome during pregnancy can be done through two types of tests. One is a prenatal screening test and the other a prenatal diagnostic test.
Prenatal screening test only estimates the chances of a fetus having this chromosomal trisomy. It is just a probability and not a confirmation. There are different kinds of screening tests.
- Blood tests: The blood tests or serum screening tests are done to analyze the blood of the mother for certain elements like alpha feta protein, inhibin A, Estriol and HCG (human gonadotrophic hormone). The results of these tests combined with the age of the mother are used to evaluate whether the developing child has a chance of having Down’s syndrome. However, it must be noted that it is still just the probability and it can be anywhere from 1/800 to 1/250. Blood tests are generally performed in first and second trimesters.
- Ultrasound: Often, the blood tests are performed in conjunction with the ultrasound. The ultrasound images help the obstetrician identify whether the physical features of the fetus are anywhere related to Down’s syndrome.
- Combined test: Researchers have come up with combined or integrated tests that include both blood test and the ultrasound. The combined test gives a higher accuracy at an early stage of pregnancy. However, they are not definitive.
Prenatal diagnostic tests:
As discussed earlier, screening tests are probability tests. The actual confirmation is done via a diagnostic analysis. Earlier, these tests were recommended for women over the age of 35 years and for those who were at higher risk of the child having this syndrome.
In these tests, a sample of either the amniotic fluid or tissue is taken and checked for extra material of chromosome 21. The results are announced anywhere between a week or two. Before any prenatal diagnostic test, the expectant couple must meet a genetic counselor to understand the risks and benefits of testing.
The different kinds of procedures are:
- Amniocentesis: As the name suggests, a sample of amniotic fluid is taken and checked for trisomy in the 21st This test is done between 14th and 18th week of pregnancy.
- Chorionic Villus Sampling: In this test, a sample of tissue is taken from the placenta and tested for the extra chromosome 21. This test is done mainly between 10th and 12th week of pregnancy.
Non-Invasive Prenatal Test (NIPT)
Generally, diagnostic tests carry a risk of miscarriage which is typically 1-2%. Therefore, doctors and couples hesitate to opt for it. However, in recent years, non-invasive prenatal screening tests like NACE have been developed. NACE is completely safe and ensures highly accurate results. Besides Down’s syndrome, NACE can detect other chromosomal anomalies such as Patau’s syndrome, Edward’s syndrome and so on.
This test involves a blood sample from the pregnant mother during the 10th week of gestation. Diagnosis relies on detection of the cell-free DNA circulating in the bloodstream via next generation sequencing technology and advanced biometric analysis. This test gives results in 7-10 days. It is completely safe, risk-free and a non-invasive test which an expectant mother can undergo without any fear. With NACE, chances of second blood extraction are just 0.1%.
NIPTs are definitely giving hope to many future parents who can undergo prenatal testing without any fear of miscarriage or any other harm to their developing baby.