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Screening for Fetal Chromosomes Antenatal Testing

Recommend 35 years by time delivery

High risk, family history

Triple screen 70% sensitivity

  • AFP dec 0.7
  • HCG inc 2.0
  • Estriol dec 0.7

Quad Screen 80%

  • Add inhibin inc 1.77 (not used in trisomy 18)

Nuchal translucency 1st trimester 11-13 weeks 70% alone

  • Fluid collection back neck fetus

NT+B HCG & PAPP-A (glycoprotein like HCG produced by trophoblasts dec 0.43)

1st trimester 85%

Combined HCG/PAPP-A & AFP/Estriol/inhibin

Integrated Screen 94-96% (NT +HCG, PAPP-A & QUAD)

Serum Integrated 85& (PAPP-A & QUAD)

NT- useful multigestation since serum screening not accurate in twins. Not available with triplets or high order multiples

  • 12-13 weeks 70% trisonomy 13, 18, 21
  • 87% Turner’s syndrome
  • 59% triploidy

Positive 1st trimester screen

  • Genetic counseling
  • Invasive testing

U/S 2nd trimester

  • Soft markers pyelectasis, shortened femur or humerus, echogenic bowel, and intracardiac echogenic focus individually do not significantly increase risk Down’s syndrome


Highest detection rate for Down’s syndrome

  • Thickened muchal fold
  • Cardiac defects

Nasal bone and tricuspid regurgitation clinical useful uncertain still research

Increased AFP > 2.0-2.5

  • NTD’s anencephaly, spine bifida, gastrichasis, omphecele

Increased acetylcholine 100% with anencephaly and open spine bifida

Dr. Khalil

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