Table 2. Birth and demographic characteristics of study participants.
| Controls (n=23 351) | ALL cases (n=8655) | AML cases (n=1292) | |
|---|---|---|---|
| Child's sex | |||
| Male | 12 516 (54%) | 4886 (57%) | 677 (52%) |
| Female | 10 835 (46%) | 3769 (44%) | 615 (48%) |
| Child's age (years) | |||
| 0–1 | 4143 (18%) | 1000 (12%) | 381 (30%) |
| 2–5 | 10 916 (47%) | 4806 (56%) | 340 (26%) |
| 6–10 | 5244 (23%) | 2013 (23%) | 330 (26%) |
| 11–14 | 2920 (13%) | 834 (10%) | 239 (19%) |
| Missing | 128 | 2 | 2 |
| Child's ethnic origin | |||
| White | 18 069 (78%) | 6723 (78%) | 978 (76%) |
| Black | 760 (3%) | 177 (2%) | 49 (4%) |
| Asian | 820 (4%) | 212 (3%) | 61 (5%) |
| Hispanic | 2476 (11%) | 965 (11%) | 152 (12%) |
| Other | 1011 (4%) | 553 (6%) | 47 (4%) |
| Missing | 215 | 25 | 5 |
| Birthweight (g) | |||
| ≤2499 | 1316 (6%) | 450 (5%) | 73 (6%) |
| 2500–3999 | 18 960 (83%) | 6866 (82%) | 1045 (82%) |
| ≥4000 | 2644 (12%) | 1068 (13%) | 156 (12%) |
| Missing | 431 | 271 | 18 |
| Gestational age (weeks) | |||
| <34 | 347 (2%) | 115 (2%) | 16 (2%) |
| 34–36 | 1005 (6%) | 431 (6%) | 66 (6%) |
| 37–38 | 3293 (18%) | 1274 (18%) | 157 (15%) |
| 39–40 | 9342 (51%) | 3624 (51%) | 556 (52%) |
| >40 | 4260 (23%) | 1650 (23%) | 276 (26%) |
| Missing | 5104 | 1561 | 221 |
| Mother's age at delivery (years) | |||
| <26 | 8179 (35%) | 2918 (34%) | 464 (36%) |
| 26–30 | 7854 (34%) | 2913 (34%) | 422 (33%) |
| 31–35 | 5081 (22%) | 1961 (23%) | 286 (22%) |
| 36–40 | 1754 (8%) | 661 (8%) | 96 (7%) |
| >40 | 306 (1%) | 98 (1%) | 22 (2%) |
| Missing | 177 | 104 | 2 |
| Parental education* | |||
| None or primary | 2082 (11%) | 1054 (13%) | 178 (15%) |
| Secondary | 7414 (40%) | 3558 (43%) | 557 (46%) |
| Tertiary | 9159 (49%) | 3644 (44%) | 473 (39%) |
| Missing | 4696 | 399 | 84 |
| Breastfeeding† | |||
| Yes | 9428 (69%) | 5049 (66%) | 468 (70%) |
| No | 4153 (31%) | 2624 (34%) | 203 (30%) |
| Missing | 9770 | 982 | 621 |
| Method of delivery | |||
| Vaginal | 18 583 (80%) | 6601 (76%) | 1020 (79%) |
| Caesarean | 4768 (21%) | 2054 (24%) | 272 (21%) |
| Type of caesarean‡ | |||
| Prelabour because of previous caesarean delivery or multiple births | 325 | 309 | 34 |
| Other or unknown | 1076 | 752 | 104 |
Data are for numbers of participants with complete data for method of delivery (%). ALL=acute lymphoblastic leukaemia. AML=acute myeloid leukaemia.
*
Data for 4230 controls, 335 ALL cases, and 66 AML cases are missing from the US (Washington) study, in which data on parental education were not obtained before 1992.
†
Data for 8499 controls, 680 ALL cases, and 128 AML cases are missing from the US (Washington) study, in which breast-feeding data were not obtained before 2003.
‡
Data are shown for the Canada, France (ESTELLE), Greece, and US (CCG) studies that had information about the indication for caesarean delivery. Only absolute counts are shown because data are for a subset of participants.