Characteristics of those included and excluded from the analytical cohort
| Variable | Level | Before HiPG availability (January 2003 to March 2009) | During HiPG availability (April 2009 to December 2010) | After HiPG availability (January 2011 to December 2013) | Full study period (January 2003 to December 2013) | ||||
| Included* | Excluded† | Included* | Excluded† | Included* | Excluded† | Included* | Excluded† | ||
| n (%) | 18 744 | 2816 | 6126 | 862 | 9719 | 1304 | 34 589 | 4982 | |
| Maternal age, n (%) | <25 years | 6359 (33.9) | 1327 (47.1) | 2039 (33.3) | 374 (43.4) | 2836 (29.2) | 523 (40.1) | 11 234 (32.5) | 2224 (44.6) |
| 25–34 years | 9684 (51.7) | 1208 (42.9) | 3272 (53.4) | 405 (47.0) | 5577 (57.4) | 651 (49.9) | 18 533 (53.6) | 2264 (45.4) | |
| 35+ years | 2701 (14.4) | 281 (10.0) | 815 (13.3) | 83 (9.6) | 1306 (13.4) | 130 (10.0) | 4822 (13.9) | 494 (9.9) | |
| Data not available, n (%) | 0 | 0‡ | 0 | 0‡ | 0 | 0‡ | 0 | 0‡ | |
| Parity, n (%) | 0 | 8077 (43.1) | 1288 (45.7) | 2670 (43.6) | 378 (43.9) | 3944 (40.6) | 585 (44.9) | 14 691 (42.5) | 2251 (45.2) |
| 1+ | 10 667 (56.9) | 1528 (54.3) | 3456 (56.4) | 484 (56.2) | 5775 (59.4) | 719 (55.1) | 19 898 (57.5) | 2731 (54.8) | |
| Data not available, n (%) | 0 | 0‡ | 0 | 0 | 0 | 0‡ | 0 | 0‡ | |
| Index of multiple deprivation group, n (%) | Most deprived | 10 820 (57.7) | 1777 (63.1) | 3566 (58.2) | 547 (63.5) | 5821 (59.9) | 794 (60.9) | 20 207 (58.4) | 3118 (62.6) |
| Moderately deprived | 4213 (22.5) | 490 (17.4) | 1330 (21.7) | 160 (18.6) | 2230 (22.9) | 220 (16.9) | 7773 (22.5) | 870 (17.5) | |
| Least deprived | 3711 (19.8) | 361 (12.8) | 1230 (20.1) | 92 (10.7) | 1668 (17.2) | 128 (9.8) | 6609 (19.1) | 581 (11.7) | |
| Data not available, n (%) | 0 | 188 (6.7)‡ | 0 | 63 (7.3)‡ | 0 | 162 (12.4)‡ | 0 | 413 (8.3)‡ | |
| Study outcomes | Mean (SD) gestational age at booking, days | 76.7 (35.8) | 106.2 (45.5)§ | 77.8 (41.3) | 99.3 (39.8)§ | 71.8 (31.8) | 95.0 (39.1)§ | 75.6 (35.8) | 102.0 (43.2)§ |
| Booked by 10 weeks, n (%) | 10 261 (54.7) | 442 (17.0)‡ | 3540 (57.8) | 152 (18.8)‡ | 6127 (63.0) | 283 (23.9)‡ | 19 928 (57.6) | 877 (19.1)‡ | |
| Booked by 18 weeks, n (%) | 17 579 (93.8) | 2012 (77.7)‡ | 5675 (92.6) | 676 (83.7)‡ | 9307 (95.8) | 1022 (86.3)‡ | 32 561 (94.1) | 3719 (81.0)‡ | |
| Booked by 25 weeks, n (%) | 18 098 (96.6) | 2397 (92.1)‡ | 5846 (95.4) | 766 (94.8) | 9477 (97.5) | 1129 (95.4)‡ | 33 421 (96.6) | 4292 (93.4)4=3 | |
| Small for gestational age, n (%) | 2346 (12.5) | 17 (8.3) | 743 (12.1) | 7 (11.5) | 1163 (12.0) | 25 (14.9) | 4252 (12.3) | 49 (11.3) | |
| Data not available on time at booking, n (%) | 0 | 214 (7.6) | 0 | 54 (6.3) | 0 | 120 (9.2) | 0 | 388 (7.8) | |
| Data not available on birth weight, n (%) | 0 | 2611 (92.7) | 0 | 801 (92.9) | 0 | 1136 (87.1) | 0 | 4548 (91.3) | |
*Women who delivered at the study hospital were known to have reached the 25th week of gestation between 1 January 2003 and 31 December 2013 and had available data on all variables of interest.
†Women who delivered at the study hospital were known to have reached the 25th week of gestation between 1 January 2003 and 31 December 2013 and did not have available data on all variables of interest.
‡Χ2 test indicates difference in distribution of levels between included and excluded at a level of P<0.05.
§T-test indicates difference in means between included and excluded at a level of P<0.05.
HiPG, Health in Pregnancy Grant.