Kozlowski 2007 GC.

Clinical features and settings	Routine referral.
Participants	6906 participants with complete outcome data. Germany ‐ gynaecologists practices. January 2000‐December 2003. Pregnant women. Median maternal age 32 years (15‐48 years), 26.4% ≥ 35 years. 11‐14 weeks' gestation.
Study design	Cohort study.
Target condition and reference standard(s)	Down's syndrome: 19 cases. Reference standard: karyotyping or follow‐up to birth.
Index and comparator tests	Maternal age. First trimester NT (FMF certified gynaecologists). First trimester free ßhCG and PAPP‐A (Kryptor analyser, Brahms). Risk cut‐point 1:300.
Follow‐up	Data on pregnancy outcome were obtained by contacting the patient or their general gynaecologist. Women without complete outcome data (36%) were excluded from the study.
Aim of study	To evaluate and compare the screening performance for fetal trisomy 21 in the first trimester of pregnancy in general gynaecologists practices and specialised centres for prenatal care in Germany.
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	Yes	146 women (including 11 with Down's syndrome) excluded as results could not be assigned to gynaecologists or prenatal centre group.