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Home > Pregnancy USG Scan > Chromosome Abnormality Screening

First Trimester Screening (The 11-13 Weeks Scan)

This scan is carried out from 11 to 13 weeks and 6 days. The scan is usually performed trans-abdominally.

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The Aim

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To assess the risks of Down’s syndrome and other chromosomal abnormalities. Each woman will be given an estimate of her individual risk for this pregnancy. This is calculated by taking into account the age and weight of the mother along with certain demographic I clinical variables, measurement of two pregnancy hormones in the mother’s blood (Free beta HCG & PAPA) and the scan findings of the thickness of the skin at the back of baby’s neck (nuchal translucency) with presence or absence of nasal bone.

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To date the pregnancy accurately.
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To assess multiple pregnancies (approximately 2% of natural and 10% of assisted conceptions) to determine if the babies share the same placenta, which can lead to problems in the pregnancy. In such cases, it would be advisable to monitor the pregnancy more closely.
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To diagnose certain major physical abnormalities of the baby which may be visible at this stage.

Second Trimester Screening (Quadruple Test)

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The Objective of Second Trimester Screening is similar to First Trimester Screening, except the fact that it is offered to women who are seen later in pregnancy after 16 weeks up to 21 weeks. Here also ultrasonographic parameters of the fetus are combined with four pregnancy hormones and Demographic variables to calculate the result. Similarly, it is reported as positive Screening (Abnormal Result) or Negative Screening (Normal Result). In the case of positive screening, further invasive testing (amniocentesis or CVS) is offered as a Diagnostic or confirmatory test for Downs Syndrome. A quadruple Test can also indicate a possible presence of a defect in the spinal cord (Spina Bifida).
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The Interpretation

Based on the calculation, the test will be reported as either Negative Screening (Normal result) or Positive Screening (Abnormal result). Parents will receive full counselling concerning the significance of the positive test and the various options for further testing. You can then decide if you wish to have an invasive diagnostic test for final confirmation of any problem in the baby.

If the test is reported as normal, it is recommended that you have an Anomaly Scan at 20 weeks to check for physical abnormalities in the baby.

The Preparation & After

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You may eat normally before.

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We will need a reasonably full bladder for the test so that you need to drink sufficient water for about an hour before the test and hold your urine.
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After the sonography is done, you will be taken for a blood sample collection in the normal way after which you may leave. The result should be available in about 5 working days.
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Preparation and procedure are similar to First Trimester Screening, except the requirement of a full bladder is not essential. The report is usually available a week after the test.
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