Transcript First Trimester Screening

First Trimester
Screening
Shannon N. Barringer, MS, CGC
Chairman, Department of Genetic Counseling
UAMS, College of Health Related Professions
Prenatal Screening: History
Down
Syndrome
ONTD
Screening
1st Δ Free
Beta
AFP Only
Free Beta
hCG
80
85
1st Δ
Papp-A
90
95
Maximizing
1st Δ Screening
NT
hCG
1975
1st Δ
Biochem/NT
NB
2000
2004
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
First Trimester Screening
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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
Markers in Pregnancy
Nuchal Translucency
•> 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!
Nuchal Translucency
Figure 10 Nuchal translucency measurement in 326 trisomy 21 fetuses plotted on the
normal range for crown–rump length (95th and 5th centiles). FMF, 2003.
Increased NT with Normal
Chromosomes
Good chance of healthy baby
90% with NT< 4.5 mm
80% with NT between 4.5 to 6.4 mm
45% with NT >6.5 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
PAPP-A and Free B-hCG
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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
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
NT, PAPP-A, and B-hCG
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Krantz, et al (1999)
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Women < 35 years
87.5% detection DS, 4.5% false positive
 100% detection Tri 18, 0.4% false positive
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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
> 15 weeks
20%
AFP & hCG
>15 weeks
60%
AFP,hCG,uE3
>15 weeks
65-70%
AFP,hCG,uE3,DIA
>15 weeks
70-75%
NT
11-14 weeks
70-80%
NT, B-hCG, PAPP-A
11-14 weeks
>85%
Other Markers and Screening?
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Nasal Bone????
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Fetal Cells in Maternal
Circulation
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Integrated Screening
Screening Protocol
Advantages of 1st Trimester
Screening
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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 outcome—referral for 2nd Δ evals.
Good time to date pregnancy accurately
NT good for multiple gestation
Limitations of First Trimester
Screening
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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
Genetic Counseling
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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
ACOG
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Screening program must
meet specific criteria:
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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