Table 2 Characteristics of twin pregnancies analysed in the Post-Birth IPI cohort
From: Interpregnancy interval and adverse birth outcomes: a population-based cohort study of twins
Characteristic | Total | Post-Birth Interpregnancy Interval n (%) | ||||||
|---|---|---|---|---|---|---|---|---|
< 6 | 6–11 | 12–17 | 18–23 | 24–59 | 60–119 | ≥ 120 | ||
n = 3531 | 223 (6.3) | 434 (12.3) | 533 (15.1) | 413 (11.7) | 1359 (38.5) | 477 (13.5) | 92 (2.6) | |
Maternal History of Preterm Birth | ||||||||
Noa | 3353 (95.0) | 207 (92.8) | 406 (93.5) | 503 (94.4) | 394 (95.4) | 1296 (95.4) | 457 (95.8) | 90 (97.8) |
Yes | 178 (5.0) | 16 (7.2) | 28 (6.5) | 30 (5.6) | 19 (4.6) | 63 (4.6) | 20 (4.2) | < 5 |
Maternal History of Early Preterm Birth | ||||||||
Noa | 3464 (98.1) | 219 (98.2) | 418 (96.3) | 524 (98.3) | 404 (97.8) | 1338 (98.5) | 469 (98.3) | 92 (100) |
Yes | 67 (1.9) | < 5 | 16 (3.7) | 9 (1.7) | 9 (2.2) | 21 (1.5) | 8 (1.7) | 0 (0) |
Maternal History of Small for Gestational age | ||||||||
Noa | 3305 (93.6) | 205 (91.9) | 397 (91.5) | 498 (93.4) | 384 (93.0) | 1291 (95.0) | 442 (92.7) | 88 (95.7) |
Yes | 226 (6.4) | 18 (8.1) | 37 (8.5) | 35 (6.6) | 29 (7.0) | 68 (5.0) | 35 (7.3) | < 5 |
Maternal History of Low Birth Weight | ||||||||
Noa | 3374 (95.6) | 211 (94.6) | 398 (91.7) | 509 (95.5) | 395 (95.6) | 1310 (96.4) | 462 (96.9) | 89 (96.7) |
Yes | 157 (4.4) | 12 (5.4) | 36 (8.3) | 24 (4.5) | 18 (4.4) | 49 (3.6) | 15 (3.1) | < 5 |
Parity | ||||||||
0 | 1999 (56.6) | 100 (44.8) | 211 (48.6) | 288 (54.0) | 251 (60.8) | 834 (61.4) | 269 (56.4) | 46 (50.0) |
1a | 883 (25.0) | 59 (26.5) | 119 (27.4) | 142 (26.6) | 99 (24.0) | 308 (22.7) | 128 (26.8) | 28 (30.4) |
2 | 363 (10.3) | 34 (15.2) | 53 (12.2) | 52 (9.8) | 32 (7.7) | 133 (9.8) | 49 (10.3) | 10 (10.9) |
≥ 3 | 286 (8.1) | 30 (13.5) | 51 (11.8) | 51 (9.6) | 31 (7.5) | 84 (6.2) | 31 (6.5) | 8 (8.7) |
Maternal Marital Status | ||||||||
Marrieda | 3072 (87) | 195 (87.4) | 386 (88.9) | 477 (89.5) | 358 (86.7) | 1192 (87.7) | 392 (82.2) | 72 (78.3) |
Other | 447 (12.7) | 28 (12.6) | 47 (10.8) | 54 (10.1) | 54 (13.1) | 164 (12.1) | 80 (16.8) | 20 (21.7) |
Missing | 12 (0.3) | 0 (0) | < 5 | < 5 | < 5 | < 5 | 5 (1.0) | 0 (0) |
Maternal Ethnicity | ||||||||
Caucasiana | 2962 (83.9) | 178 (79.8) | 349 (80.4) | 440 (82.6) | 353 (85.5) | 1151 (84.7) | 414 (86.8) | 77 (83.7) |
Indigenous Australian | 292 (8.3) | 23 (10.3) | 40 (9.2) | 47 (8.8) | 34 (8.2) | 114 (8.4) | 27 (5.7) | 7 (7.6) |
All Other | 277 (7.8) | 22 (9.9) | 45 (10.4) | 46 (8.6) | 26 (6.3) | 94 (6.9) | 36 (7.5) | 8 (8.7) |
Maternal Age (years) at Twins’ Birth | ||||||||
< 24 | 1164 (33.0) | 66 (29.6) | 104 (24.0) | 147 (27.6) | 132 (32.0) | 452 (33.3) | 207 (43.4) | 56 (60.9) |
25-29a | 1273 (36.1) | 75 (33.6) | 154 (35.5) | 170 (31.9) | 147 (35.6) | 509 (37.5) | 185 (38.8) | 33 (35.9) |
30–34 | 838 (23.7) | 55 (24.7) | 121 (27.9) | 158 (29.6) | 107 (25.9) | 317 (23.3) | 77 (16.1) | < 5 |
≥ 35 | 256 (7.3) | 27 (12.1) | 55 (12.7) | 58 (10.9) | 27 (6.5) | 81 (6.0) | 8 (1.7) | 0 (0) |
Maternal Occupation Status Scaleb (quintiles) | ||||||||
0–20 | 1016 (28.8) | 75 (33.6) | 129 (29.7) | 140 (26.3) | 115 (27.8) | 370 (27.2) | 152 (31.9) | 35 (38.0) |
> 20–40 | 633 (17.9) | 43 (19.3) | 70 (16.1) | 96 (18.0) | 67 (16.2) | 248 (18.2) | 93 (19.5) | 16 (17.4) |
> 40–60 | 551 (15.6) | 28 (12.6) | 74 (17.1) | 91 (17.1) | 71 (17.2) | 206 (15.2) | 69 (14.5) | 12 (13.0) |
> 60–80 | 181 (5.1) | 10 (4.5) | 28 (6.5) | 28 (5.3) | 23 (5.6) | 69 (5.1) | 22 (4.6) | < 5 |
> 80-100a | 436 (12.3) | 15 (6.7) | 59 (13.6) | 75 (14.1) | 53 (12.8) | 190 (14.0) | 40 (8.4) | < 5 |
Missing | 714 (20.2) | 52 (23.3) | 74 (17.1) | 103 (19.3) | 84 (20.3) | 276 (20.3) | 101 (21.2) | 24 (26.1) |
Birth Year | ||||||||
1980-1989a | 997 (28.2) | 79 (35.4) | 106 (24.4) | 138 (25.9) | 113 (27.4) | 394 (29.0) | 139 (29.1) | 28 (30.4) |
1990–1999 | 1084 (30.7) | 73 (32.7) | 132 (30.4) | 151 (28.3) | 120 (29.1) | 399 (29.4) | 161 (33.8) | 48 (52.2) |
2000–2009 | 1150 (32.6) | 46 (20.6) | 138 (31.8) | 172 (32.3) | 128 (31.0) | 475 (35.0) | 175 (36.7) | 16 (17.4) |
2010–2015 | 300 (8.5) | 25 (11.2) | 58 (13.4) | 72 (13.5) | 52 (12.6) | 91 (6.7) | < 5 | 0 (0) |
Index of Relative Socioeconomic Disadvantagec (quintiles) | ||||||||
1 (most disadvantaged) | 773 (21.9) | 48 (21.5) | 93 (21.4) | 112 (21.0) | 82 (19.9) | 300 (22.1) | 117 (24.5) | 21 (22.8) |
2 | 737 (20.9) | 57 (25.6) | 82 (18.9) | 91 (17.1) | 64 (15.5) | 290 (21.3) | 131 (27.5) | 22 (23.9) |
3 | 688 (19.5) | 46 (20.6) | 87 (20.0) | 99 (18.6) | 96 (23.2) | 254 (18.7) | 84 (17.6) | 22 (23.9) |
4 | 619 (17.5) | 31 (13.9) | 87 (20.0) | 97 (18.2) | 75 (18.2) | 237 (17.4) | 79 (16.6) | 13 (14.1) |
5 (least disadvantaged)a | 577 (16.3) | 30 (13.5) | 70 (16.1) | 107 (20.1) | 74 (17.9) | 223 (16.4) | 62 (13.0) | 11 (12.0) |
Missing | 137 (3.9) | 11 (4.9) | 15 (3.5) | 27 (5.1) | 22 (5.3) | 55 (4.0) | < 5 | < 5 |