Wednesday, July 5, 2017

Down’s Syndrome Screening- A Brief Introduction

Down’s syndrome screening
The screening procedures offered currently in most of the countries are listed here. Each consists of a risk assessment based on maternal age and a scan performed in the first trimester or a blood test in the first or second trimester or a combination of scans and blood test.

Triple test
Done in early second trimester (14–20 completed weeks). This test is based on the measurement of

  1. α-fetoprotein,
  2. unconjugated oestriol (uE3) and 
  3. hCG (either total hCG or free β-hCG)

together considering the maternal age.

Nuchal translucency scan
A first trimester (11–13 weeks) test is based on the measurement of the fold of skin on the back of the fetal neck.

Quadruple test
Early second trimester (14–21 weeks) test is based on the measurement of

  1. α-fetoprotein, 
  2. uE3, 
  3. free β-hCG (or total hCG) and 
  4. inhibin-A 

together considering the maternal age.

Combined test
Late first trimester (10–13 weeks) test is based on combining NT measurement with free β-hCG, pregnancy associated plasma protein-A (PAPP-A) and maternal age.

Integrated test
This is the integration of different screening markers measured at different stages of pregnancy into a single test result. Unless otherwise qualified, ’Integrated test’ refers to the integration of NT measurement and PAPP-A in the first trimester with serum α-fetoprotein, β-hCG and uE3 in the second.

TheNICE Guideline– Antenatal Care, Routine Carefor the Healthy Pregnant Woman stated that by April 2007,
pregnant women should be offered screening for Down’s Syndrome with a test which provides a detection rate of >75% and a false-positive rateof <3%. These performance measures should be age-standardized and based on cutoff of 1 in 250 at term. These guidelines were based on the study of
nearly 50,000 singleton pregnancies in women where the most effective, safe and cost-effective method of screening for Down’s syndrome using NT, maternal serum and urine markers in the first and second trimester of pregnancy and maternal age in various combinations were analysed.

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