Input variables (volumes and probabilities)
| Variable | Mean (%) | Uncertainty | Source |
|---|---|---|---|
| Screening uptake | 78.87 | Scenario analysis: 90% | Belgian data (NIHDI) |
| Testing uptake (ie, screening+invasive test without prior screening) | 79.74 | Belgian data (NIHDI) | |
| Current screening accuracy | Scenario analysis+ | Belgian data (AML) | |
| Sensitivity | 72.54 | β (103; 39) | |
| Specificity | 95.03 | β (117 144; 6121) | |
| NIPT | Literature10 | ||
| Sensitivity | 99.3 | 95% CI 98.2 to 99.8% (β (6; 1.06); 2.5%: 0.982; 97.5%: 0.998) | |
| Specificity | 99.84 | 95% CI 99.69 to 99.92% (β (3; 1.014); 2.5%: 0.9969; 97.5%: 0.9992) | |
| NIPT test failure rate | Expert opinion plus literature10 | ||
| First test (at week 12) | 4 | Minimum–maximum 3–7% (β (2; 6); minimum: 0.03; maximum: 0.07) | |
| Second test (at week 13) | 2 | Minimum–maximum: 1–3% (β (2; 2); minimum: 0.01; maximum: 0.03) | |
| Probability of having an invasive test (after a positive screening test or NIPT) | 87.5 | Minimum–maximum: 0.8–0.95% (β (2; 2); minimum: 0.8; maximum: 0.95) | Assumption and model fitting plus literature11 |
| Number of invasive tests without prior screening | 3212 | Conditional β distribution (313.9; 1000; 84.1; 1814) | Belgian NIHDI data and model fitting; literature36 |
| Invasive testing (CVS or amniocentesis) | / | Considered as the gold standard | |
| Sensitivity | 100 | ||
| Specificity | 100 | ||
| Procedure-related fetal loss after invasive test | 1 | Minimum–maximum: 0.5–2% (β (2; 4); minimum: 0.005; maximum: 0.02) | Literature14 |
| Hospitalisation for amniotic fluid leakage after invasive test | 1 | Minimum–maximum: 0.5–2% (β (2; 4); minimum: 0.005; maximum: 0.02) | Literature13 |
| Pregnancy termination after T21 diagnosis | 95.45 | β (42; 2) | Belgian data and literature11 17 |
| Spontaneous miscarriage | Literature6 7 | ||
| Miscarriage all (p) | 0.05, 0.025, 0.015 at weeks 10, 12 and 14, respectively* | ||
| T21 miscarriage (p) | 0.36, 0.3, 0.25 at weeks 10, 12 and 14, respectively | ||
*Rounded numbers extracted from a published figure.7
AML, Algemeen Medisch Laboratorium bvba; CVS, chorionic villus sampling; NIHDI, National Institute for Health and Disability Insurance; NIPT, non-invasive prenatal test.