Trisomy is a condition in which an extra copy of a chromosome is present in the cell that may result in severe mental / physical retardation.
Down syndrome, also known as Trisomy 21, is a genetic disorder that occurs in approximately 1 of 800 live births. Down syndrome is associated with mild to moderate learning disabilities, developmental delays, characteristic facial features, and low muscle tone in early infancy. Individuals with Down syndrome also have heart defects, leukemia, early onset of Alzheimer’s disease, gastro-intestinal problems and other health issues.
Edward’s Syndrome, also known as Trisomy 18, is a genetic disorder caused by the presence of all or part of an extra 18th chromosome. It is the second most common autosomal trisomy, after Down syndrome that carries to term. Edward Syndrome occurs in 1 of 6000 live births and around 80% of those affected are female. The majority of fetuses with the syndrome die before birth. The syndrome has a very low survival rate, resulting from heart abnormalities, kidney malfunctions, and other internal organ disorders.
Patau Syndrome, also known as Trisomy 13 or Trisomy D, is a chromosomal abnormality in which a patient has an additional chromosome due to a non-disjunction of chromosome during meiosis. The extra chromosome 13 disrupts the normal course of development, causing heart and kidney defects. Patau syndrome affects somewhere between 1 in 10,000 and 1 in 21,700 live births.
All couples have approximately 2% risk of having a child with a birth defect.
Over 70% of Down syndrome infants are born to women under 35 years of age
|Mother’s Age||Changes of Down Syndrome|
|25||1 in 1250 mothers|
|30||1 in 840 mothers|
|35||1 in 356 mothers|
|40||1 in 94 mothers|
|45||1 in 24 mothers|
Advantages of first trimester combined screening over Triple Test
Screening Model offered by Suburban Diagnostics
Both First Trimester and Second Trimester Screening Tests are performed on FMF (Fetal Medicine Foundation) accredited instruments and reagents. The system has been fully validated and all the calculation methods, algorithms and values are supported by current published literature.
Interpretation of Prenatal Screening
Low Risk: If the risk of identified chromosomal abnormalities like Down syndrome, based on the patients age, biochemical levels & ultrasound measurements are lower than a specified limit (1:250 for Down syndrome), the patient is considered to be at a low risk of having a Down syndrome baby. However, a low risk does not necessarily rule out the possibility of a pregnancy with chromosomal abnormalities. With a low risk report the doctor may not advice further testing.
High Risk: If risk as per the screening test result is more than the specified limit (1:250), the patient is considered to be at a relatively high risk of having a Down syndrome baby. However, a high risk result from a prenatal screening test does not confirm trisomy hence it should be followed by a confirmatory test.
If a screening test report indicates a high risk of having a Down syndrome baby, one of the following optional tests may be advised:
Chorion Villus Sampling
Confirmatory tests are invasive and they carry a slight risk of miscarriage. Screening therefore helps ensure that invasive tests are done only for high risk patients.