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Fruit of the Womb
Fruit of the Womb

Composite Results are the Strength of First Trimester Screening for Aneuploidy

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The reader below faces what appears to be a growing dilemma for patients (and their providers) in the laboratory reporting of results from first trimester screening for aneuploidy. The data that supports this screening modality has always emphasized that the power of the screening test is in the COMPOSITE test results and NOT the individual ‘analytes’ which include the actual nuchal translucency measurement along with the hCG, PAPP-A, and other factors.

As can be seen from the ‘results’, she is being given risk results for trisomy 21 (Down syndrome) that range between 1 in 47 ( based on the biochemical screening alone) to 1 in 612 (based on the ultrasound evaluation of the baby). The COMPOSITE (and in my mind the KEY information) is the 1 in 292 “adjusted risk” but as a patient (and even as a doctor), how are you going to sit with reconciling the great disparity in risks in a way that will help you make the most unbiased decisions possible regarding further evaluation of the baby and, particularly, the invasive diagnostic studies which carry their own inherent risks…?

Singapore Mother has left a new comment on your post "Understanding Interpretation of First Trimester Sc...":

Dear Dr. T,

I am 39 years old. The results of my test are as follow:

@ 12 weeks + 0 days

Crown-rump length (CRL) 56.1mm
Nuchal translucency (NT) 1.4mm

Maternal Serum Biochemistry
Free B-hcg 129.4 IU/I = 1.993 MoM
PAPP-A 0.557 IU/I = 0.578 MoM

Trisomy 21
1:122 (Background risk)
1:612 Adjusted risk (US)
1:47 Adjusted risk (BC)
1:292 (Adjusted risk)

Kindly please shed some light... Thank you so much!


To Singapore Mother July 7: Personally, I think it is VERY confusing and unfair to present the data to patients in this way. The strength of the first trimester screening is in the COMPOSITE results and NOT the individual tests - and yet you were given the risk assessment based on those individual tests. All that can do is make you worry about the greates ‘risk’ estimate and any laboratory that does this should be banned from first trimester screening because they are presenting 'data' out of both sides of their mouths without providing adequate counseling to the patients or realistic expectations as to what balanced information most providers can offer! Albeit, this is just my opinion.

The long and short of your results are that you have a 1 in 292 risk of Down syndrome which is less than half your age alone risk. Some laboratories will still report this as "screen positive" because it falls below there cut off, but that also means your baby has a 291 out of 292 chance of being chromosomally normal. If the odds still worry you, then you can have either a genetic amniocentesis done or simply have an expert sonogram done at 18-20 weeks. If the latter is 'normal' your a priori risk is reduced by at least another 50%. Best wishes and let us know how things turn out.
Dr T
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