Table 1. Sociodemographic characteristics of the study cohort.
| Characteristics | Post-Birth Interpregnancy Interval | |||||||
|---|---|---|---|---|---|---|---|---|
| n = 32,324 | ||||||||
| <6 | 6–11 | 12–17 | 18–23 | 24–35 | 36–47 | 48–60 | ||
| n = 1561 | n = 5333 | n = 7008 | n = 5623 | n = 6870 | n = 3737 | n = 2192 | ||
| Child | ||||||||
| Sex of Child | Male | 759 (48.6) | 2714 (50.9) | 3468 (49.5) | 2858 (50.8) | 3549 (51.7) | 1911 (51.1) | 1105 (50.4) |
| Femalea | 802 (51.4) | 2619 (49.1) | 3540 (50.5) | 2765 (49.2) | 3321 (48.3) | 1826 (48.9) | 1087 (49.6) | |
| Age Category at Time of AEDC Completionb (years) | 1 | 262 (16.8) | 916 (17.2) | 1217 (17.4) | 976 (17.4) | 1189 (17.3) | 677 (18.1) | 380 (17.3) |
| 2a | 1177 (75.4) | 3951 (74.1) | 5178 (73.9) | 4208 (74.8) | 5141 (74.8) | 2747 (73.5) | 1618 (73.8) | |
| 3 | 122 (7.8) | 466 (8.7) | 613 (8.7) | 439 (7.8) | 540 (7.9) | 313 (8.4) | 194 (8.9) | |
| Pregnancy and Birth | ||||||||
| Maternal Smoking Status during pregnancy | Noa | 1069 (68.5) | 4497 (84.3) | 6149 (87.7) | 4880 (86.8) | 5919 (86.2) | 3089 (82.7) | 1767 (80.6) |
| Smoked | 492 (31.5) | 836 (15.7) | 859 (12.3) | 743 (13.2) | 951 (13.8) | 648 (17.3) | 425 (19.4) | |
| Preterm birth | ≥37 weeksa | 1434 (91.9) | 5011 (94.0) | 6627 (94.6) | 5272 (93.8) | 6426 (93.5) | 3491 (93.4) | 2037 (92.9) |
| <37 weeks | 127 (8.1) | 322 (6.0) | 381 (5.4) | 351 (6.2) | 444 (6.5) | 246 (6.6) | 155 (7.1) | |
| Small for gestational age | Noa | 1409 (90.3) | 4888 (91.7) | 6430 (91.8) | 5172 (92.0) | 6312 (91.9) | 3416 (91.4) | 1978 (90.2) |
| Yes | 152 (9.7) | 445 (8.3) | 578 (8.2) | 451 (8.0) | 558 (8.1) | 321 (8.6) | 214 (9.8) | |
| Parity | First Birtha | 772 (49.5) | 3297 (61.8) | 4651 (66.4) | 3642 (64.8) | 4151 (60.4) | 2031 (54.3) | 1114 (50.8) |
| Second Birth | 388 (24.9) | 1209 (22.7) | 1476 (21.1) | 1295 (23.0) | 1835 (26.7) | 1143 (30.6) | 712 (32.5) | |
| Third Birth | 209 (13.4) | 488 (9.2) | 506 (7.2) | 423 (7.5) | 525 (7.6) | 364 (9.7) | 228 (10.4) | |
| Fourth Birth | 84 (5.4) | 175 (3.3) | 204 (2.9) | 136 (2.4) | 206 (3.0) | 125 (3.3) | 87 (4.0) | |
| ≥Fifth Birth | 108 (6.9) | 164 (3.1) | 171 (2.4) | 127 (2.3) | 153 (2.2) | 74 (2.0) | 51 (2.3) | |
| Maternal Age at time of Child’s Birth (years) | <20 | 170 (10.9) | 317 (5.9) | 348 (5.0) | 314 (5.6) | 442 (6.4) | 343 (9.2) | 241 (11.0) |
| 20–24 | 438 (28.1) | 1130 (21.2) | 1259 (18.0) | 1026 (18.2) | 1416 (20.6) | 905 (24.2) | 598 (27.3) | |
| 25–29a | 348 (22.3) | 1608 (30.2) | 2282 (32.6) | 1860 (33.1) | 2109 (30.7) | 1016 (27.2) | 518 (23.6) | |
| 30–34 | 127 (8.1) | 574 (10.8) | 753 (10.7) | 500 (8.9) | 583 (8.5) | 237 (6.3) | 109 (5.0) | |
| 35–39 | 458 (29.3) | 1662 (31.2) | 2322 (33.1) | 1886 (33.5) | 2280 (33.2) | 1227 (32.8) | 720 (32.8) | |
| ≥40 | 20 (1.3) | 42 (0.8) | 44 (0.6) | 37 (0.7) | 40 (0.6) | 9 (0.2) | 6 (0.3) | |
| Sociodemographic | ||||||||
| Language other than English Spoken at Home by Child | Noa | 1371 (87.8) | 4757 (89.2) | 6346 (90.6) | 5099 (90.7) | 6039 (87.9) | 3209 (85.9) | 1857 (84.7) |
| Yes | 190 (12.2) | 576 (10.8) | 662 (9.4) | 524 (9.3) | 831 (12.1) | 528 (14.1) | 335 (15.3) | |
| Ethnicity of Child | Non-Indigenousa | 1311 (84) | 4886 (91.6) | 6570 (93.8) | 5267 (93.7) | 6399 (93.1) | 3410 (91.2) | 1957 (89.3) |
| Indigenous Australian | 250 (16.0) | 447 (8.4) | 438 (6.3) | 356 (6.3) | 471 (6.9) | 327 (8.8) | 235 (10.7) | |
| Attended Preschool | No | 134 (8.6) | 375 (7.0) | 487 (6.9) | 376 (6.7) | 411 (6.0) | 247 (6.6) | 147 (6.7) |
| Yesa | 1328 (85.1) | 4700 (88.1) | 6257 (89.3) | 5053 (89.9) | 6183 (90.0) | 3336 (89.3) | 1939 (88.5) | |
| Unavailable | 99 (6.3) | 258 (4.8) | 264 (3.8) | 194 (3.5) | 276 (4.0) | 154 (4.1) | 106 (4.8) | |
| Maternal Marital status at Time of Child’s Birth | Married (inc. de facto) a | 1321 (84.6) | 4797 (89.9) | 6405 (91.4) | 5120 (91.1) | 6159 (89.7) | 3229 (86.4) | 1854 (84.6) |
| All other | 232 (14.9) | 495 (9.3) | 553 (7.9) | 452 (8.0) | 655 (9.5) | 483 (12.9) | 329 (15.0) | |
| Unavailable | 8 (0.5) | 41 (0.8) | 50 (0.7) | 51 (0.9) | 56 (0.8) | 25 (0.7) | 9 (0.4) | |
| Maternal Occupation Statusc | 0-<20 (lowest status) | 447 (28.6) | 993 (18.6) | 1069 (15.3) | 832 (14.8) | 1114 (16.2) | 771 (20.6) | 517 (23.6) |
| ≥20-<40 | 414 (26.5) | 1293 (24.2) | 1616 (23.1) | 1336 (23.8) | 1769 (25.7) | 1036 (27.7) | 633 (28.9) | |
| ≥40-<60 | 296 (19.0) | 1189 (22.3) | 1671 (23.8) | 1362 (24.2) | 1678 (24.4) | 845 (22.6) | 476 (21.7) | |
| ≥60-<80 | 103 (6.6) | 489 (9.2) | 730 (10.4) | 647 (11.5) | 659 (9.6) | 306 (8.2) | 143 (6.5) | |
| ≥80–100a (highest status) | 126 (8.1) | 1040 (19.5) | 1559 (22.2) | 1178 (20.9) | 1273 (18.5) | 514 (13.8) | 241 (11.0) | |
| Unavailable | 175 (11.2) | 329 (6.2) | 363 (5.2) | 268 (4.8) | 377 (5.5) | 265 (7.1) | 182 (8.3) | |
| Paternal Occupation Statusc | 0-<20 (lowest status) | 201 (12.9) | 466 (8.7) | 498 (7.1) | 429 (7.6) | 589 (8.6) | 354 (9.5) | 250 (11.4) |
| ≥20-<40 | 731 (46.8) | 2296 (43.1) | 2888 (41.2) | 2282 (40.6) | 2878 (41.9) | 1615 (43.2) | 1005 (45.8) | |
| ≥40-<60 | 151 (9.7) | 641 (12.0) | 928 (13.2) | 802 (14.3) | 924 (13.4) | 534 (14.3) | 265 (12.1) | |
| ≥60-<80 | 168 (10.8) | 865 (16.2) | 1173 (16.7) | 931 (16.6) | 1140 (16.6) | 514 (13.8) | 293 (13.4) | |
| ≥80–100a (highest status) | 111 (7.1) | 708 (13.3) | 1109 (15.8) | 878 (15.6) | 915 (13.3) | 423 (11.3) | 179 (8.2) | |
| Unavailable | 199 (12.7) | 357 (6.7) | 412 (5.9) | 301 (5.4) | 424 (6.2) | 297 (7.9) | 200 (9.1) | |
| Accessibility and Remoteness Index of Australiad | 1 (Least Remote)a | 1022 (65.5) | 3631 (68.1) | 4914 (70.1) | 3983 (70.8) | 4883 (71.1) | 2628 (70.3) | 1519 (69.3) |
| 2 | 207 (13.3) | 591 (11.1) | 757 (10.8) | 586 (10.4) | 717 (10.4) | 380 (10.2) | 214 (9.8) | |
| 3 | 183 (11.7) | 603 (11.3) | 704 (10.0) | 563 (10.0) | 668 (9.7) | 375 (10.0) | 225 (10.3) | |
| 4 | 83 (5.3) | 262 (4.9) | 354 (5.1) | 290 (5.2) | 324 (4.7) | 184 (4.9) | 116 (5.3) | |
| 5 (Most Remote) | 46 (2.9) | 146 (2.7) | 173 (2.5) | 118 (2.1) | 187 (2.7) | 119 (3.2) | 85 (3.9) | |
| Unavailable | 20 (1.3) | 100 (1.9) | 106 (1.5) | 83 (1.5) | 91 (1.3) | 51 (1.4) | 33 (1.5) | |
| Index of Relative Socioeconomic Disadvantagee | 1 (Most Disadvantaged) | 446 (28.6) | 1029 (19.3) | 1113 (15.9) | 904 (16.1) | 1202 (17.5) | 757 (20.3) | 473 (21.6) |
| 2 | 354 (22.7) | 968 (18.2) | 1228 (17.5) | 959 (17.1) | 1198 (17.4) | 744 (19.9) | 483 (22.0) | |
| 3 | 286 (18.3) | 1007 (18.9) | 1324 (18.9) | 1043 (18.5) | 1366 (19.9) | 718 (19.2) | 412 (18.8) | |
| 4 | 259 (16.6) | 1121 (21) | 1618 (23.1) | 1315 (23.4) | 1505 (21.9) | 804 (21.5) | 400 (18.2) | |
| 5 (Least Disadvantaged)a | 202 (12.9) | 1083 (20.3) | 1598 (22.8) | 1320 (23.5) | 1508 (22) | 670 (17.9) | 403 (18.4) | |
| Unavailable | 14 (0.9) | 125 (2.3) | 127 (1.8) | 82 (1.5) | 91 (1.3) | 44 (1.2) | 21 (1.0) | |
aReference group for regression analysis.
bAge categories classified as; 1) ≥3 years 10 months to <5 years and one month, 2) ≥5 years and one month to <5 years and 10 months, 3) ≤5 years and 10 months.
cMaternal and Paternal Occupation Status are classified into five categories in line with the Australian Socioeconomic Index 2006 (AUSEI06); low AUSEI06 values represent low-status occupations.
dCategorised as nationally defined into five classes of remoteness; 1 = Major Cities of Australia (least remote) to 5 = Very Remote Australia (most remote).
eCategorised as nationally defined quintiles (1 = most disadvantaged to 5 = least disadvantaged); as quintiles are defined nationally (rather than within study population), numbers within each category vary from 20% of the total.