Niemimaa 2001a.

Clinical features and settings	Routine screening.
Participants	2515 participants. Finland ‐ primary care centres and maternity clinics of hospitals. During 1999. Pregnant women, 17.5% ≥ 35 years. 10‐13 weeks' gestation.
Study design	Prospective cohort.
Target condition and reference standard(s)	Down's syndrome: 8 cases. Reference standards: invasive testing (patients considered high risk based on NT screening) or follow‐up to birth.
Index and comparator tests	Maternal age. First trimester NT (≥ 3 mm) (64% of women) (method not described). Fresh serum tested for: First trimester free ßhCG and PAPP‐A (Wallac analytes and 1st trimester risk calculation programme Maternal weight correction). Risk cut‐point 1:250.
Follow‐up	Follow‐up data from maternity clinics and the National Research and Development Centre for Welfare and Health. Test negative patients followed up by contacting all maternity clinics and the National Research and Development Centre for Welfare and Health. Unclear if follow‐up information was obtained in all cases.
Aim of study	To evaluate efficacy of combining first trimester maternal serum and fetal NT measurement in screening for Down's syndrome in Finland.
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	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.