# 4.b How are the results presented?

## Description

This article is from the Pregnancy
Screening FAQ, by Lynn Gazis-Sax (gazissax@netcom.com) with
numerous contributions by others.

# 4.b How are the results presented?

The results may be presented in a number of ways. It is important to

understand what your numbers mean. Ask your caregiver to explain.

The triple screen might be given as a probability such as: "based on

maternal age your risk of Down's is 1/390 --- when the levels of AFP, HCG

and uE3 are also taken into account, your risk is 1/14000. Based on AFP

levels, your risk of neural tube defects is 1/1400."

Or the results might simply be positive/negative, or normal/abnormal. You

will probably want to know exactly what that means. Ask. In fact, there is

controversy as to what "abnormal" means. Try to find out what your lab

considers abnormal. They are working from the more detailed probability

information.

I think that it is becoming more common for the results to be given as

probabilities, which are more meaningful than a simple "positive/negative"

which is impossible to interpret. Probabilities can still be kind of scary

to interpret though.

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Addition by Dr. Tim Reynolds:

Probabilities can be very misleading and are often 'over-interpreted by

obstetricians as a way of avoiding doing amniocenteses. The usual risk cut

off in the UK is 1 in 300: Using this cut off about 1 in every 50 amnios

will yeild an abnormality. Some obstetricians use 1 in 150 as a cut off.

This halves the number of amnios they do. The rationale for using this cut

off is that the risk of abortion due to amnio is about 1 in 150. Since in

the 1 in 300 group you expect 1 in 50 amnios to give an abnormal result it

is evident that their argument is specious.

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