Table 2.
Derivation of study population: very preterm births (VPTBs) selected for chart abstraction and controls from the linked prenatal screening livebirth cohort of 346 456 by race-ethnic group, California Very Preterm Birth Study
| Inclusion steps | White (n = 110,861) | Hispanic (n = 217,264) | Black (n = 18,331) | |||
|---|---|---|---|---|---|---|
| VPTBs | Controls | VPTBs | Controls | VPTBs | Controls | |
| n (%)a | n (%)a | n (%)a | n (%)a | n (%)a | n (%)a | |
| 1. Gestational age <32 weeks (<34 weeks for Blacks) for VPTBs; controls ≥ 37 weeks | 929 (NA) | 99 981 (NA) | 2439 (NA) | 194 676 (NA) | 774 (NA) | 15 582 (NA) |
| 2. Singletons (based on birth certificate) | 691 (74.4) | 98 778 (98.8) | 2085 (85.5) | 193 266 (99.3) | 643 (83.1) | 15 421 (99.0) |
| 3. Birthweight <2500 g for VPTBs and ≥ 2500 g for controls | 674 (97.5) | 97 672 (98.9) | 1942 (93.1) | 190 462 (98.5) | 590 (91.8) | 14 908 (96.7) |
| 4. Link to Newborn Screening Specimen | 597 (88.6) | 96 783 (99.1) | 1733 (89.2) | 188 973 (99.2) | 517 (87.6) | 14 624 (98.1) |
| 5. Maternal specimens collected by regional laboratory #1 (Blacks also include regional laboratory #2) | 458 (76.7) | 78 893 (81.5) | 1123 (64.8) | 124 885 (66.1) | 517 (100) | 14 624 (100) |
| 6. Born in Los Angeles, Orange, Riverside, San Bernardino or San Diego counties | 445 (97.2) | 77 579 (98.3) | 1086 (96.7) | 118 829 (95.2) | 407 (78.7) | 11 643 (79.6) |
| 7. No. of eligible controls not excluded for complications of pregnancy or delivery | NA (NA) | 74 632 (96.2) | NA (NA) | 116 008 (97.6) | NA (NA) | 11 237 (96.5) |
| 8. First pregnancy during study period | 421 (94.6) | 63 879 (85.6) | 1035 (95.3) | 104 845 (90.4) | 384 (94.3) | 10 433 (92.8) |
| 9. No birth defects identified by CBDMP registry | 405 (96.2) | 63 874 (100) | 1026 (99.1) | 104 839 (100) | 380 (99.0) | 10 427 (99.9) |
| 10. Stored maternal specimens available | 394 (97.3) | 63 265 (99.0) | 1003 (97.8) | 104 061 (99.3) | 330 (86.8) | 9116 (87.4) |
| 11. First 385 VPTBs of Whites and Hispanics, all available Black VPTBs, and random samples of controls | 385 (NA) | 200 (NA) | 385 (NA) | 253b (NA) | 330 (NA) | 343 (NA) |
a
% of remaining.
b
Because of expansion of the study region after the shipping and DNA extraction of Hispanic specimens, 53 extra Hispanic controls were sampled to represent the expanded geographical region.
NA, not applicable; CBDMP, California Birth Defects Monitoring Program.