Pajkrt 1998.

Clinical features and settings	Routine screening
Participants	1473 participants The Netherlands tertiary maternity unit June 1994 to March 1997 Pregnant women Mean age 31.4 years (SD 5.7), 24% ≥ 35 years Singleton pregnancies 10‐14 weeks' gestation
Study design	Prospective cohort
Target condition and reference standard(s)	Down's syndrome: 9 cases Reference standards: prenatal karyotyping offered to patients considered high risk or maternal anxiety (conducted in 24%) or follow‐up to birth
Index and comparator tests	Maternal age NT (FMF method, Hitachi machines, 6 sonographers instructed to take 'sufficient time') Risk cut‐point ≥ 3 mm
Follow‐up	Follow‐up to outcome assessment in the delivery room. 68 women (4.4%) were excluded from the study due to loss to follow‐up
Aim of study	To evaluate the effectiveness of NT measurement in the detection of trisomy 21 in a low‐risk population
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	Unclear	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	Yes	Unsuccessful NT measurement in 4.3%
Withdrawals explained? All tests	No	No details of withdrawals given