Table 1 Characteristics of twin pregnancies analysed in the IPI cohort
From: Interpregnancy interval and adverse birth outcomes: a population-based cohort study of twins
Characteristic | Total | Interpregnancy Interval n (%) | ||||||
|---|---|---|---|---|---|---|---|---|
< 6 | 6- 11 | 12–17 | 18–23 | 24–59 | 60–119 | ≥ 120 | ||
n = 6336 | 293 (4.6) | 797 (12.6) | 1106 (17.5) | 1017 (16.1) | 2300 (36.3) | 652 (10.3) | 171 (2.7) | |
Maternal History of Preterm Birth | ||||||||
Noa | 5564 (87.8) | 207 (70.6) | 685 (86.1) | 985 (89.1) | 909 (89.4) | 2045 (88.9) | 589 (90.3) | 144 (84.2) |
Yes | 772 (12.2) | 86 (29.4) | 112 (14.1) | 121 (10.9) | 108 (10.6) | 255 (11.1) | 63 (9.7) | 27 (15.8) |
Maternal History of Early Preterm Birth | ||||||||
Noa | 6066 (95.7) | 240 (81.9) | 757 (95.1) | 1066 (96.4) | 979 (96.3) | 2227 (96.8) | 634 (97.2) | 163 (95.3) |
Yes | 270 (4.3) | 53 (18.1) | 40 (5.0) | 40 (3.6) | 38 (3.7) | 73 (3.2) | 18 (2.8) | 8 (4.7) |
Maternal History of Small for Gestational age | ||||||||
Noa | 5444 (85.9) | 216 (73.7) | 681 (85.6) | 969 (87.6) | 889 (87.4) | 1997 (86.8) | 550 (84.4) | 142 (83.0) |
Yes | 892 (14.1) | 77 (26.3) | 116 (14.6) | 137 (12.4) | 128 (12.6) | 303 (13.2) | 102 (15.6) | 29 (17.0) |
Maternal History of Low Birth Weight | ||||||||
Noa | 5712 (90.2) | 210 (71.7) | 710 (89.2) | 1010 (91.3) | 935 (91.9) | 2099 (91.3) | 601 (92.2) | 147 (86.0) |
Yes | 624 (9.8) | 83 (28.3) | 87 (10.9) | 96 (8.7) | 82 (8.1) | 201 (8.7) | 51 (7.8) | 24 (14.0) |
Parity | ||||||||
1a | 3553 (56.1) | 126 (43) | 445 (55.9) | 690 (62.4) | 639 (62.8) | 1279 (55.6) | 292 (44.8) | 82 (48.0) |
2 | 1679 (26.5) | 75 (25.6) | 193 (24.2) | 260 (23.5) | 247 (24.3) | 642 (27.9) | 215 (33.0) | 47 (27.5) |
≥ 3 | 1104 (17.4) | 92 (31.4) | 159 (20.0) | 156 (14.1) | 131 (12.9) | 379 (16.5) | 145 (22.2) | 42 (24.6) |
Maternal Marital Status | ||||||||
Marrieda | 5775 (91.1) | 251 (85.7) | 718 (90.2) | 1042 (94.2) | 960 (94.4) | 2107 (91.6) | 561 (86.0) | 136 (79.5) |
Other | 541 (8.5) | 41 (14.0) | 74 (9.3) | 60 (5.4) | 53 (5.2) | 190 (8.3) | 89 (13.7) | 34 (19.9) |
Missing | 20 (0.3) | < 5 | 5 (0.6) | < 5 | < 5 | < 5 | < 5 | < 5 |
Maternal Ethnicity | ||||||||
Caucasiana | 5405 (85.3) | 222 (75.8) | 667 (83.8) | 977 (88.3) | 899 (88.4) | 1946 (84.6) | 546 (83.7) | 148 (86.5) |
Indigenous Australian | 452 (7.1) | 43 (14.7) | 66 (8.3) | 57 (5.2) | 53 (5.2) | 165 (7.2) | 53 (8.1) | 15 (8.8) |
All Other | 479 (7.6) | 28 (9.6) | 64 (8.0) | 72 (6.5) | 65 (6.4) | 189 (8.2) | 53 (8.1) | 8 (4.7) |
Maternal Age (years) at Twins’ Birth | ||||||||
< 24 | 788 (12.4) | 83 (28.3) | 149 (18.7) | 161 (14.6) | 117 (11.5) | 258 (11.2) | 20 (3.1) | 0 (0) |
25-29a | 1869 (29.5) | 94 (32.1) | 298 (37.4) | 316 (28.6) | 348 (34.2) | 637 (27.7) | 168 (25.8) | 8 (4.7) |
30–34 | 2193 (34.6) | 72 (24.6) | 221 (27.8) | 411 (37.2) | 351 (34.5) | 825 (35.9) | 259 (39.7) | 54 (31.6) |
≥ 35 | 1486 (23.5) | 44 (15.0) | 129 (16.2) | 218 (19.7) | 201 (19.8) | 580 (25.2) | 205 (31.4) | 109 (63.7) |
Maternal Occupation Status Scaleb (quintiles) | ||||||||
0–20 | 2279 (36.0) | 115 (39.2) | 284 (35.7) | 372 (33.6) | 364 (35.8) | 870 (37.8) | 240 (36.8) | 34 (19.9) |
> 20–40 | 1105 (17.4) | 60 (20.5) | 124 (15.6) | 158 (14.3) | 157 (15.4) | 396 (17.2) | 155 (23.8) | 55 (32.2) |
> 40–60 | 1016 (16.0) | 23 (7.8) | 121 (15.2) | 191 (17.3) | 163 (16.0) | 372 (16.2) | 105 (16.1) | 41 (24.0) |
> 60–80 | 422 (6.7) | 13 (4.4) | 40 (5.0) | 84 (7.6) | 72 (7.1) | 151 (6.6) | 47 (7.2) | 15 (8.8) |
> 80-100a | 815 (12.9) | 30 (10.2) | 90 (11.3) | 174 (15.7) | 142 (14.0) | 299 (13.0) | 67 (10.3) | 13 (7.6) |
Missing | 699 (11.0) | 52 (17.7) | 138 (17.3) | 127 (11.5) | 119 (11.7) | 212 (9.2) | 38 (5.8) | 13 (7.6) |
Birth Year | ||||||||
1980-1989a | 1013 (16.0) | 65 (22.2) | 168 (21.1) | 199 (18.0) | 170 (16.7) | 371 (16.1) | 40 (6.1) | 0 (0) |
1990–1999 | 1818 (28.7) | 74 (25.3) | 211 (26.5) | 306 (27.7) | 312 (30.7) | 664 (28.9) | 213 (32.7) | 38 (22.2) |
2000–2009 | 2125 (33.5) | 92 (31.4) | 248 (31.2) | 362 (32.7) | 315 (31.0) | 756 (32.9) | 261 (40.0) | 91 (53.2) |
2010–2015 | 1380 (21.8) | 62 (21.2) | 170 (21.4) | 239 (21.6) | 220 (21.6) | 509 (22.1) | 138 (21.2) | 42 (24.6) |
Index of Relative Socioeconomic Disadvantagec (quintiles) | ||||||||
1 (most disadvantaged) | 1242 (19.6) | 103 (35.2) | 152 (19.1) | 182 (16.5) | 172 (16.9) | 452 (19.7) | 140 (21.5) | 41 (24.0) |
2 | 1231 (19.4) | 68 (23.2) | 170 (21.4) | 196 (17.7) | 171 (16.8) | 437 (19.0) | 156 (23.9) | 33 (19.3) |
3 | 1130 (17.8) | 52 (17.7) | 145 (18.2) | 201 (18.2) | 178 (17.5) | 392 (17.0) | 121 (18.6) | 41 (24.0) |
4 | 1238 (19.5) | 32 (10.9) | 157 (19.7) | 231 (20.9) | 216 (21.2) | 461 (20.0) | 112 (17.2) | 29 (17.0) |
5 (least disadvantaged)a | 1268 (20.0) | 28 (9.6) | 139 (17.5) | 244 (22.1) | 238 (23.4) | 485 (21.1) | 108 (16.6) | 26 (15.2) |
Missing | 227 (3.6) | 10 (3.4) | 34 (4.3) | 52 (4.7) | 42 (4.1) | 73 (3.2) | 15 (2.3) | < 5 |