Perni 2006.

Clinical features and settings	Routine screening
Participants	4615 participants USA ‐ single institution January 2003 to September 2004 Pregnant women Singleton pregnancies Mean age 33.0 years (IQR 31.0‐36.0) 10‐13 weeks' gestation
Study design	Retrospective cohort
Target condition and reference standard(s)	Down's syndrome: 22 cases Reference standards: CVS or amniocentesis. Cytogenetic testing in cases of miscarriage. Follow‐up to birth.
Index and comparator tests	Maternal First trimester NT (FMF methods) First trimester PAPP‐A and free ßhCG (dried blood spots, methodology described elsewhere)
Follow‐up	Outcome information from computerised medical record review. Numbers of patients lost to follow‐up not reported
Aim of study	To evaluate the performance of maternal age, fetal NT, PAPP‐A and free ßhCG for aneuploidy screening
Notes	Appears that all cases of Down’s were diagnosed prenatally by karyotyping
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	Unclear	Unclear if 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