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Screen Positive First Trimester Combined Test Results
Counselling Issues
If CVS Is Unavailable
Do Not Offer First Trimester Combined And Stepwise Sequential Testing
Women With Positive Screening Results
Offer Definitive Fetal Karyotype Determination By CVS
Alternative
Secondary Screening Using A Maternal Plasma-Based Test For Cell-Free Fetal DNA
Screen Positive Integrated Test Results
Screen Negative First Trimester Or Integrated Test Results
The Cut-Off Often Higher Than That Of The Combined Or Quadruple Test
Typical Cut-Off : A Midpregnancy Risk Of Down Syndrome Of ≥1 In 100
A FPR Of 1 To 2 % And Odds Of Down Syndrome Of About 1 In 5 To 1 In 10.
Amniocentesis Is The Diagnostic Test
Patient's Risk Of Having A Baby With Down Syndrome
Is Less Than
A Specified Cut-Off Level
Meaning
Patient's Risk Provided In The Report (Eg, Down Syndrome Risk 1 In 900)
This Number Should Be Given To The Patient
Does Not Exclude The Possibility Of Down Syndrome
No Further Testing Is Recommended
Detection Of Structural Anomalies
??
Does It Obviate The Need For Second Trimester Fetal Assessment
Including
Second Trimester USG Examination Or AFP Screening For NTD
TRISOMY 18 RISK ASSESSMENT
Prevalence Is Three To Five-Fold Higher In The First And Second Trimesters
About 1 In 8000 Births
90 % Of Affected Infants Die Within The First Year Of Life
50 % Die Within The First Week
TRISOMY 18 RISK ASSESSMENT
First Trimester Analyte Pattern Characteristic
Very Low Beta-Hcg And Very Low PAPP-A, And Increased NT Measurement
FPR Kept Very Low (Less Than 0.5 Percent)
So That
Only A Small Number Of Very High Risk Women
Will Be Offered Invasive Diagnostic Testing
Integrated Test
Highly Efficient In Identifying Cases Of Trisomy 18
DR 90 % At FPR Of 0.1 Percent
OTHER ANEUPLOIDIES
Screening For Such Defects Is Not Warranted --- Low Prevalence
Many Of These Defects Are Either Lethal
Fetus Is Often Lost Early In Pregnancy
Or
Mild
Risk Of Invasive Testing Is Questionable
OTHER ANEUPLOIDIES
Identified
As
Being At High Risk For Down Syndrome Or Trisomy 18,
Or
Presented With Cystic Hygroma In The First Trimester
ADVERSE PREGNANCY OUTCOME
Predictive Of Obstetrical Complications
But
The Predictive Value Of These Tests Is Low
VARIABLES THAT AFFECT PERFORMANCE AND INTERPRETATION
Selection of Risk Cut-off
Midpregnancy Versus Term Risk
Effect of Maternal Age
Prior Pregnancy History
Method Of Gestational Age Determination
Adjustments To MoM
• Race
• Body Weight
• Multiple gestation
• Diabetes mellitus
• In vitro fertilization
• Previous false positive result
• Smoking
Screen Positive First Trimester Combined Test Results
Refers To
Risk Of Having Child With Down Syndrome = Or > A Specific Cut-Off Level
Typical Cut-Off
Term Risk Of Down Syndrome Of ≥1 In 300
Associated With
FPR Of About 5 % And Odds Of Down Syndrome Of About 1 In 20
Septated Cystic Hygroma :: 50 % Risk Of Aneuploidy
Nuchal Translucency ≥3 Mm :: 17 % Risk Of Aneuploidy
Also Associated With Other
Structural Malformations
FIRST TRIMESTER COMBINED TEST
INTEGRATED TESTS
Testing Uses Markers Measured In Both First And Second Trimesters
PAPP-A
Between 9 And 13 Weeks
Between 10 And 13 Weeks
USG Measurement Of NT + Estimation Of GA By CRL
Second Trimester
Quadruple Test Markers AFP,Ue3, Inhibin A, Beta-Hcg)
Six Marker Values Are Used Together With Maternal Age
INTEGRATED TESTS
An 85 % DR At A 1 % FPR
If A 90 % DR Is The Target, The FPR Will Be 2 %
Substantially Lower FPR Than Combined Or Quadruple Test
Decrease No Of Patients Who Are Anxious
Fewer Procedure-Related Miscarriages
Also Detects Trisomy 18
Serum Integrated Test
Full Integrated Test, But Without USG Measurement Of NT
Step-Wise Sequential Screening
First Trimester Portion Of The Integrated Screen
Contingent Sequential Screening
Women At Very High Risk (Eg, >1 In 50) After First Trimester Testing
OFFER : Immediate Invasive Prenatal Diagnosis
Women At Low Risk (Eg, <1 In 2000) After First Trimester Testing Provide : With Their Risk Estimate -- No Any Additional Testing
Women At Intermediate Risk ( Between 1 In 50 And 1 In 2000) Second Trimester Blood Draw To Complete The Integrated Test
A Cost-Effective Approach
No Consensus On Thresholds
COMPARATIVE DATA FROM PROSPECTIVE TRIALS
The Serum, Urine And Ultrasound Screening Study (SURUSS)
And
First And Second Trimester Evaluation Of Risk (FASTER) Trial
The Most Efficient Screening Test (High DR, Low FPR)
Procedure-Related Unaffected Fetal Loss : 9 Per 100,000 Women Screened V/S
Combined Test Or A Second Trimester Quadruple Test : 45 Per 100,000
If NT Testing Is Not Available :: Next Most Efficient Choice
Quadruple Test :: The Best Available Option
For Women Who Present For Prenatal Care In Second Trimester
First Trimester Combined Screening
Reasonable Approach Who Desire Earliest Possible Screening And Diagnosis
Stepwise Sequential Screening - A Variant Of The Integrated Test
A Valuable Alternative
Reports Very High Risk Results In The First Trimester
Elevated In Pregnancies Affected With Down Syndrome
Lower In Pregnancies Affected With Fetal Down Syndrome
Operator Expertise And Quality Of Equipment
Proper Training And Ongoing Quality Management
• Explanation Of Difference Between Screening Test And Diagnostic Test
• Screening Sensitivity And Specificity Compared To Diagnostic Testing
• Description Of Performance Of Various Screening Tests
• Option Of Diagnostic Testing Instead Of Screening
• Risks Associated With Prenatal Diagnosis
• Psychological Implications Of Prenatal Screening And Diagnosis
• Implications Of Having A Child With Down Syndrome
• Detection Rate Of Other Chromosomal Abnormalities And Implications Of Having Child
• Information About Length Of Time Necessary To Obtain Results From Screening And
• Information About Pregnancy Termination.
Diagnostic Testing
Dual Marker
Findings Which Warrants Immediate Diagnostic Work-Up
• Nuchal Translucency ≥3 mm :: 17 % Risk Of Aneuploidy
• Septated Cystic Hygroma :: 50 % Risk Of Aneuploidy
Also Associated With Other
Structural Malformations
• A previous pregnancy complicated by fetal trisomy
• At least one major or two minor fetal structural anomalies in
the current pregnancy
• Chromosomal translocation, inversion, or aneuploidy in Patient
or Partner