First%20Trimester%20Screening

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First Trimester Screening
Shannon N. Barringer, MS, CGC Chairman,
Department of Genetic Counseling UAMS, College of
Health Related Professions
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Prenatal Screening History
Down Syndrome AFP Only
1st ? Free Beta
1st ? Biochem/NT
ONTD Screening
Maximizing 1st ? Screening
NT
hCG
Free Beta hCG
1st ? Papp-A
NB
1975 80 85 90 95 2000 2004
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First Trimester Screening On the Horizon

• GOALS of this screen
• To increase sensitivity, decrease false-positive
  rates
• To decrease number of unnecessary invasive
  prenatal diagnosis tests.
• NOT to increase number of elective abortions.
• U/S measurements (NT) and free B-hCG, PAPP-A

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First Trimester Screening

• A method to identify women at risk for having an
  aneuploid fetus from the general population
• Also can identify other birth defects such as
  congenital heart defects and diaphragmatic hernia
  
• Performed during 11-14 weeks gestation
• Patient Preferences and earlier diagnosis/
  reassurance

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Markers in Pregnancy
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Nuchal Translucency

• gt 3mm 30 risk of aneuploidy
• 50-85 detection, 4.5 false positive
• Also associated with CHD, skeletal abnormalities,
  and diaphragmatic hernia

Measurements must be performed by certified
individual!
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Nuchal Translucency
Figure 10  Nuchal translucency measurement in 326
trisomy 21 fetuses plotted on the normal range
for crownrump length (95th and 5th centiles).
FMF, 2003.
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Increased NT with Normal Chromosomes

• Good chance of healthy baby
• 90 with NTlt 4.5 mm
• 80 with NT between 4.5 to 6.4 mm
• 45 with NT gt6.5 mm
• 20-30 have adverse pregnancy outcome
• IUFD, PTD, low birth weight
• Genetic syndromes, skeletal dysplasias, CHD
• Risk appears to be proportionate to aneuploid
  risk
• Still provide 18-20 week U/S and echocardiogram

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PAPP-A and Free B-hCG

• 60-68 detection of DS
• 90 detection of Tri 18
• 4.5 false positive rate
• Also drawn at 11-14 weeks
• Some centers quote 87 detection of DS when
  combined with maternal age
• If both PAPP-A and B-hCG are very low MoM
  Increased risk for tri 18, triploidy, fetal
  anomalies or perinatal complications

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PAPP-A and Free B-hCG
On average, baby with trisomy 21 will have 2.0
Mom for B-hCG and 0.4 MoM PAPP-A
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NT, PAPP-A, and B-hCG

• Krantz, et al (1999)
• Women lt 35 years
• 87.5 detection DS, 4.5 false positive
• 100 detection Tri 18, 0.4 false positive
• Women 35 years or older
• 92 detection of DS, 14.3 false positive
• 100 detection Tri 18, 1.4 false positive

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Detection Rates-Fetal Down Syndrome
Marker
Timing
Detection Rate
AFP ALONE gt 15 weeks 20
AFP hCG gt15 weeks 60
AFP,hCG,uE3 gt15 weeks 65-70
AFP,hCG,uE3,DIA gt15 weeks 70-75
NT 11-14 weeks 70-80
NT, B-hCG, PAPP-A 11-14 weeks gt85
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Other Markers and Screening?

• Nasal Bone????
• Fetal Cells in Maternal Circulation
• Integrated Screening

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Screening Protocol
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Advantages of 1st Trimester Screening

• Information earlier, more options
• Reduce number of invasive procedures
• May identify other severe anomalies (or risk for)
  at time of scan and increased risk of adverse
  pregnancy outcomereferral for 2nd ? evals.
• Good time to date pregnancy accurately
• NT good for multiple gestation

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Limitations of First Trimester Screening

• Accuracy of NT strongly dependant on experience
  of ultrasonographers
• Not all women enter prenatal care in time for
  screening
• Results of screen may arrive too late for CVS or
  early amnio
• Extra cost for first trimester ultrasound
• Can not detect NTD or AWD, still need MSAFP

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Genetic Counseling

• Nondirective counseling is vital
• Informed consent is vital
• The patient should undergo detailed counseling
  regarding first versus second trimester screening
• All diagnostic testing options should be
  discussed

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ACOG

• Screening program must meet specific criteria
• Trained, certified, monitored sonographers
  perform NT
• NT alone is not sufficient, biochemistry must be
  included
• Comprehensive genetic counseling must be offered
• Access to diagnostic testing if abnormal screen
  results
• Rigorous continual evaluations