Christiansen 2005.

Clinical features and settings	Screening programmes for syphilis and Down's syndrome.
Participants	108 participants: 27 cases of Down's syndrome and 81 controls. Denmark ‐ Statens Serum Institute. Dates not specified. 5‐11 weeks' gestation.
Study design	Case‐control study.
Target condition and reference standard(s)	Down's syndrome: 27 cases (18 diagnosed in 2nd trimester, 9 at birth). Reference standard: karyotyping.
Index and comparator tests	Maternal age. First trimester (week 11‐14) NT. Frozen samples tested for: First trimester (week 5‐11) 1T Inhibin A (dimer assay kit MCA 950KZZ, Serotec). First trimester (week 5‐11) ßhCG (available for some samples). First trimester (week 5‐11) PAPP‐A (available for some samples) (combined PAPP‐A and B‐hCG TrIFMA assay). Risk cut‐points of 1:100, 1:250 and 1:400. Performance assessed with SPlus algorithm.
Follow‐up	All diagnosis were verified by karyotyping.
Aim of study	To investigate whether first trimester Inhibin A can be used in the first trimester for Down's syndrome screening.
Notes	Identified through the Danish central cytogenetic registry as part of quality assurance programme.
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.
Partial verification avoided? All tests	Yes	All women had a reference standard.
Differential verification avoided? All tests	Yes	All women had the same reference standard.
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 NT results.
Index test results blinded? All tests	Unclear	Unclear if all index tests 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.