First Trimester Screening

The following was a letter to the local national newspaper The Star that was not published.

Dear Editor

I find the article "New scan in town' StarTwo 10.7.2007, Women, T16 somewhat misleading and I like to share the following points to assist pregnant women in their decision on the appropriate test that they may decide.

1. Firstly it is not a new scan in town as it has been offered by several Medical Centres for over a year now.

2. The Nuchal Translucency (NT) scan and the First Trimester Screening Test ( NT, free beta HcG and PAPP-A) is a SCREENING test and hence it is not diagnostic which means if the NT scan showed an abnormal result one has to still undergo an amniocentesis to confirm the diagnosis.

3. The NT scan has its limitations as it is dependent on the accuracy of the gestational age of the fetus, the abdominal size of the pregnant women, the training of the operator, the type of machines used and the strict adherence to guidelines on measurements of the NT. In comparison there are less limitations on the Amniocentesis procedure.

4. The second-trimester "quad" screening using four serum markers (MSAFP, total or beta-hCG, unconjugated estradiol, and serum inhibin A) offer a comparable detection rate to the First Trimester Screening ( NT, free beta HcG and PAPP-A) which is 79% detection rate of Down Syndrome with a 5% false positive rate. In comparison Amniocentesis detects 100% of Down Syndrome with a 0% false positive rate.

5. The First Trimester Screening Test is a screening test ONLY for Down Syndrome and in some instances for Trisomy 13 and 18. The Amniocentesis detects ALL known Chromosomal defects

6. The Integrated Test incorporating the First and Second Trimester blood markers have a 88% detection rate which is HIGHER than the First Trimester Screening and it DOES NOT incorporate NT.

7. The nasal bone is more difficult to detect and seems to have a less prominent role in identifying the fetus at risk for Down Syndrome due to its lower detection rate

8. A large recent trial (FASTER) has demonstrated that the miscarriage rate from amniocentesis is indeed only 0.15% and not 0.5% as always believed, Thus making it a very safe option.

9. There are several prenatal test available and there is not one that fits all including the NT. The tests have to be individualized according to the patients risk profile.

There is no doubt that NT and First Trimester screening have an important role in screening for Down Syndrome but pregnant women should be given accurate information about the detection rates and false positive rates of any Down's syndrome screening test and the further diagnostic tests that may be offered. They should also be offered BOTH screening and diagnostic test as options and the woman's right to accept or decline the test should be made clear.

Lastly the authors and the people appearing in the feature should declare their association with the centres offering the test to accurately reflect the unbiasness of the reporting.

DR GUNASEGARAN