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Sequential Pathways of Testing After First-Trimester Screening for Trisomy 21

In Reply:

We thank Dr. Malone for his interest in our article.¹ The BUN Study² offered the combined first-rimester screening test as a research protocol, and as such the results were provided in that context and not as the standard of care. We further advised the physician that second-trimester multiple-marker screening should still be offered.

Comparing first- and second-trimester screening protocols was never presented as a primary objective of the BUN study. Women who accepted second-trimester multiple-marker screening did so in the context of their own physician's practice. Their blood was drawn and results reported to them by their physicians, not through our study. Therefore, as had been suggested by Dr. Malone, it would have been completely inappropriate to recommend to physicians that they use the Down syndrome risk calculated in our research study as a patient's a priori risk in their clinical practices.

The vast majority of the Discussion section of our current article iterates the limitations of the data we presented. Nowhere in the current article is it suggested that we propose the sequence of screening steps described in the Methods section as a new screening paradigm. We do, however, suggest that the fact that 6 of 7 Down syndrome cases missed by first-trimester screening were picked up by the second-trimester screen underscores the need to further investigate various screening paradigms.

Dr. Malone states that his "preferred" method of sequential screening will give the patient the benefit of first-trimester results. However, under his proposed protocol, the patient is not informed of the first-trimester results in the first trimester. We feel strongly that results should be reported as they become available, for these reasons:

• Earlier diagnosis of aneuploidy can be offered and, upon diagnosis, earlier and safer termination can be made available.
  
• Even with Dr. Malone's assertion that his method yields the highest detection and lowest false-positive rates, the reality is that many women do not return for the second-trimester test.^2,3
  
• There is published evidence to show that disclosing first-trimester results will actually not greatly diminish the detection rate or increase false positivity.⁴
  
• Dr. Malone states that in a screening population in which first-trimester results have been disclosed, 70–90% of Down syndrome cases will have been removed from the population when this group returns at 15 weeks. In the BUN Study, however, only 213 of 813 screen-positive patients had an early invasive procedure; only 22 of 51 Down syndrome cases were removed (43.1%).² All women with a positive result do not automatically choose an early invasive procedure.
  

In a screening paradigm in which results are disclosed at each testing interval, women are given useful information in a timely fashion that empowers them with the tools for informed decision making.

doi:10.1097/01.AOG.0000153372.65818.90

REFERENCES

1. Platt LD, Greene N, Johnson A, Zachary J, Thom E, Krantz D, et al. Sequential pathways of testing after first-trimester screening for trisomy 21. Obstet Gynecol 2004;104:661–6.[Abstract/Free Full Text]

2. Wapner R, Thom E, Simpson JL, Pergament E, Silver R, Filkins K, et al. First-trimester screening for trisomies 21 and 18. N Engl J Med 2003;349:1405–13.[Abstract/Free Full Text]

3. Wald NJ, Rodeck C, Hackshaw AK, Walters J, Chitty L, Mackinson AM. First and second trimester antenatal screening for Down's syndrome: the results of the Serum, Urine and Ultrasound Screening Study (SURUSS). J Med Screen 2003;10:56–104.[Free Full Text]

4. Wright D, Bradbury I, Benn P, Cuckle H, Ritchie K. Contingent screening for Down syndrome is an efficient alternative to non-disclosure sequential screening. Prenat Diagn 2004;24:762–6.[Medline]

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