Wright 2008.

Clinical features and settings	Routine screening
Participants	37,488 participants with complete outcome data UK ‐ single centre July 1999 ‐ July 2005 Pregnant women Singleton pregnancies Median maternal age 35.2 years (16‐52 years) 11‐13 weeks' gestation
Study design	Cohort
Target condition and reference standard(s)	Down's syndrome: 264 cases Reference standards: karyotyping or follow‐up to birth
Index and comparator tests	Maternal age First trimester NT First trimester PAPP‐A and free ßhCG (Kryptor system, Brahms AG)
Follow‐up	Maternal characteristics and test results were recorded in a computer database and karyotype results and details on pregnancy outcomes added as they became available. Women without complete outcome data (n = 1231, 3.2%) were excluded from the study
Aim of study	To examine the validity of methods used to derive patient‐specific risks form NT measurements
Notes
Table of Methodological Quality
Item	Authors' judgement	Description
Representative spectrum? All tests	Yes	Routine screening of typical pregnant population
Acceptable reference standard? All tests	Yes	Karyotyping or follow‐up to birth
Partial verification avoided? All tests	Yes	All women received a reference standard
Differential verification avoided? All tests	No	Choice of reference standard depended on index test results
Incorporation avoided? All tests	Yes	Reference standard was independent of the index test
Reference standard results blinded? All tests	No	Reference standard interpreted with knowledge of index test results
Index test results blinded? All tests	Yes	Index test interpreted without knowledge of reference standard results
Relevant clinical information? All tests	Yes	Information available as would be in standard clinical practice
Uninterpretable results reported? All tests	No	No details given for test failures/uninterpretable measurements
Withdrawals explained? All tests	No	No details of withdrawals given