De Graaf 1999a.
| Clinical features and settings | High‐risk referral for invasive testing. | |
| Participants | 292 participants (207 participants before 14 weeks' gestation): 37 cases and 255 controls matched for maternal age (within 2 years), gestational age (within 2 weeks) and duration of sample storage (within 2 months) The Netherlands ‐ single centre. 1994‐1997. Pregnant women. 9‐15 weeks' gestation (in a few cases, blood samples for serum testing taken at 15‐19 weeks). |
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| Study design | Case‐control study. | |
| Target condition and reference standard(s) | Down's syndrome: 37 cases (30 affected pregnancies in women with serum testing enrolled before 14 weeks' gestation). Reference standards: CVS or amniocentesis. |
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| Index and comparator tests | Maternal age. First trimester NT (FMF methods) with cut off > 3 mm. Frozen serum samples tested for: First trimester free ßhCG and AFP (DELFIA dual labelled time resolved fluorescent assay). First trimester serum PAPP‐A (DELFIA research assay (CR61‐105)). First trimester serum AFP. |
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| Follow‐up | 100% karyotyping. | |
| Aim of study | To determine the expected detection rate and false positive rate for Down's syndrome achievable by early pregnancy screening with combined measurements of serum PAPP‐A, free beta hCG and fetal NT, with the addition of AFP. | |
| Notes | ||
| Table of Methodological Quality | ||
| Item | Authors' judgement | Description |
| Representative spectrum? All tests | Yes | Selective testing of high‐risk women as done in practice. |
| 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 some index test 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 | Yes | Failed to measure NT in 11 control women. |
| Withdrawals explained? All tests | No | No details of withdrawals given. |