ACC Prenatal Retrospective Audit:

The Clinical Value of Prenatal Karyotyping for 'Down Screen Positive' women

This audit was performed from data supplied by UK cytogenetics laboratories. In all about 29 laboratories perform >38,000 prenatal karyotype tests per annum. Most of these laboratories offer FISH or PCR as well at least for some cases.

The audit consisted of two parts.

PART 1: Laboratories were asked to supply prenatal karyotypes for the last five years based on reason for referral. Namely: ABSCAN, Raised Maternal Age, Serum Screen Positive (with or without NT), BIO/DNA, CARRIER, PREVIOUS PATIENT HISTORY, PREVIOUS FAMILY HISTORY and OTHER. 

The purpose of this part of the audit was to ask the following question:

If karyotyping was to be replaced by PCR or FISH for 'Down Screen Positive' women (serum screen positive with or without NT and raised maternal age) how often would clinically significant chromosome abnormalities that would not be expected to be detected by PCR or FISH for 13, 18, 21 be missed?

PART 2: Laboratories were asked to state whether they were currently offering a rapid diagnostic test by PCR or FISH as well as karyotyping. Laboratories were asked to provide data for the last three years or from the inception of this service whichever was the greater time period.

The purpose of this part of the audit was to ask the following question:

How efficient was PCR or FISH for the detection of trisomy 13,18,21 compared to conventional karyotyping over this time period? 

Where there was discordance between the two methods for any given sample was this due to false positive or false negative results for either technology or differences in success rates between PCR or FISH and karyotyping?

Amniotic Fluid and Chorion Villus Datasets for Part 1 and a summary of the Part 2 results are attached.