TABLE 1.
Cohort demographics
| Demographic | Total cohort N = 55,344 | MZ by SNP‐cfDNA N = 16,673 | DZ by SNP‐cfDNA N = 38,671 | p‐value* | |
|---|---|---|---|---|---|
| GA at draw, completed weeks median, (5th, 95th percentile) | 12.0 (10.0, 21.0) | 12.0 (10.0, 21.0) | 12.0 (10.0, 21.0) | p > 0.999 | |
| MA (years) median, (5th, 95th percentile) | 32.0 (22.0, 40.0) | 31.0 (21.0, 40.0) | 32.0 (23.0, 40.0) | p < 0.001 | |
| MW (pounds)† median, (5th, 95th percentile) | 163.0 (114.0, 266.0)† | 154.0 (110.2, 243.0) | 167 (115.5, 272.0) | p < 0.001 | |
| IVF (n/N, %) | 538/55,344 (1.0%) | 59/16,673 (0.3%) | 479/38,671 (1.2%) | p < 0.001 | |
| Fetal fraction (%)# median (5th, 95th percentile) | 11.7% (5.1, 21.7) | 11.6% (5.3, 21.3) | 11.7% (5.0, 21.9) | p = 0.96 | |
| Ethnicity (% of cohort) | MZ versus DZ | All group comparison | |||
|---|---|---|---|---|---|
| White, non‐Hispanic or Latino | 22.6% | 22.3% | 22.7% | p = 0.31 | p < 0.001 |
| Black or African American, non‐Hispanic or Latino | 9.1% | 6.5% | 10.1% | p < 0.001 | |
| Hispanic or Latino | 7.3% | 9.5% | 6.4% | p < 0.001 | |
| Asian, non‐Hispanic or Latino | 1.7% | 2.4% | 1.3% | p < 0.001 | |
| Other, non‐Hispanic or Latino | 2.4% | 2.8% | 2.2% | p < 0.001 | |
| Unknown | 56.9% | 56.4% | 57.2% | p = 0.082 | |
Note: Demographic information abstracted from requisition for cohort of patients with reported zygosity.
Abbreviations: GA, gestational age, MA, maternal age, MW maternal weight, and ethnicity. Demographic information was analyzed by zygosity and across the total cohort. GA, MA, and MW are reported as median (5th and 95th percentile). *p‐value calculated for comparison of MZ and DZ twins. #Total fetal fraction is combined for DZ twins, a single fetal fraction is reported for MZ twins, and †Cases with reasonable weights were included (70–700 pounds).