| 2014 survey N  = 4571 | 2018 survey N  = 4509 | 2020 survey N  = 4611 | |||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 | n | % | OR | 95%CI | aOR a | 95% CI | n | % | OR | 95%CI | aOR a | 95% CI | n | % | OR | 95%CI | aOR a | 95% CI |
Total n % (95%CI) | 3082 | 79.8 | (78.4, 81.1) | Â | Â | 3509 | 75.3 | (73.7, 76.9) | Â | Â | 3637 | 77.1 | (75.6, 78.6) | Â | Â | |||
Age of Mother | ||||||||||||||||||
 16–19 | 70 | 79.7 | 1.01 | 0.56, 1.81 | 0.99 | 0.53, 1.85 | 50 | 77.8 | 1.13 | 0.52, 2.47 | 1.21 | 0.49, 2.99 | 36 | 79.9 | 1.10 | 0.47, 2.56 | 1.23 | 0.50, 3.04 |
 20–24 | 359 | 81.3 | 1.11 | 0.83, 1.50 | 1.17 | 0.85, 1.60 | 280 | 76.3 | 1.03 | 0.75, 1.42 | 1.15 | 0.79, 1.65 | 294 | 82.1 | 1.27 | 0.89, 1.80 | 1.22 | 0.83, 1.79 |
 25–29 | 852 | 82.2 | 1.18 | 0.95, 1.48 | 1.21 | 0.95, 1.52 | 845 | 76.1 | 1.02 | 0.81, 1.28 | 1.08 | 0.85, 1.38 | 896 | 77.5 | 0.95 | 0.76, 1.18 | 0.95 | 0.76, 1.19 |
 30–34 | 1076 | 79.6 | 1 |  | 1 |  | 1342 | 75.7 | 1 |  | 1 |  | 1430 | 78.3 | 1 |  | 1 |  |
 35–39 | 585 | 77.4 | 0.88 | 0.70, 1.10 | 0.80 | 0.63, 1.01 | 796 | 73.4 | 0.89 | 0.72, 1.10 | 0.94 | 0.76, 1.17 | 819 | 73.1 | 0.75 | 0.61, 0.93 | 0.75 | 0.60, 0.94 |
 40 +  | 141 | 69.5 | 0.58 | 0.42, 0.82 | 0.58 | 0.41, 0.83 | 196 | 72.6 | 0.85 | 0.62, 1.18 | 0.84 | 0.60, 1.19 | 162 | 68.2 | 0.59 | 0.41, 0.85 | 0.70 | 0.48, 1.02 |
Ethnicity | ||||||||||||||||||
 White | 2559 | 81.4 | 1 |  | 1 |  | 3060 | 80.4 | 1 |  | 1 |  | 3207 | 81.8 | 1 |  | 1 |  |
 Mixed | 54 | 73.9 | 0.64 | 0.34, 1.24 | 0.63 | 0.33, 1.20 | 80 | 80.5 | 1.00 | 0.55, 1.84 | 1.14 | 0.62, 2.09 | 69 | 62.1 | 0.36 | 0.23, 0.58 | 0.40 | 0.24, 0.64 |
 Asian | 272 | 72.7 | 0.61 | 0.47, 0.79 | 0.61 | 0.46, 0.81 | 185 | 54.1 | 0.29 | 0.22, 0.38 | 0.32 | 0.24, 0.43 | 234 | 57.5 | 0.30 | 0.23, 0.39 | 0.35 | 0.27, 0.45 |
 Black | 101 | 77.4 | 0.78 | 0.51, 1.20 | 0.91 | 0.55, 1.48 | 62 | 58.6 | 0.34 | 0.22, 0.55 | 0.49 | 0.30, 0.82 | 75 | 60.0 | 0.33 | 0.21, 0.52 | 0.49 | 0.31, 0.77 |
 Other | 14 | 75.0 | 0.68 | 0.24, 1.93 | 0.70 | 0.23, 2.08 | 40 | 56.3 | 0.31 | 0.17, 0.56 | 0.33 | 0.18, 0.59 | 14 | 54.9 | 0.27 | 0.12, 0.63 | 0.31 | 0.12, 0.75 |
IMD | ||||||||||||||||||
 1 (least advantaged) | 561 | 78.5 | 1.00 | 0.77, 1.29 | 1.19 | 0.90, 1.58 | 521 | 68.9 | 0.55 | 0.42, 0.70 | 0.75 | 0.57, 0.98 | 520 | 73.2 | 0.72 | 0.56, 0.92 | 0.82 | 0.62, 1.08 |
 2 | 659 | 80.5 | 1.13 | 0.88, 1.45 | 1.30 | 0.99, 1.70 | 683 | 75.9 | 0.78 | 0.61, 0.99 | 0.98 | 0.75, 1.28 | 685 | 75.0 | 0.79 | 0.61, 1.01 | 0.91 | 0.70, 1.19 |
 3 | 638 | 80.4 | 1.12 | 0.87, 1.44 | 1.15 | 0.89, 1.49 | 735 | 76.7 | 0.81 | 0.64, 1.03 | 0.90 | 0.70, 1.15 | 768 | 80.4 | 1.07 | 0.84, 1.37 | 1.13 | 0.88, 1.45 |
 4 | 611 | 81.4 | 1.20 | 0.93, 1.55 | 1.20 | 0.92, 1.56 | 787 | 79.0 | 0.93 | 0.74, 1.17 | 0.99 | 0.77, 1.27 | 858 | 79.9 | 1.04 | 0.82, 1.31 | 0.99 | 0.77, 1.26 |
 5 (most advantaged) | 613 | 78.5 | 1 |  | 1 |  | 783 | 80.2 | 1 |  | 1 |  | 806 | 79.2 | 1 |  | 1 |  |
Education | ||||||||||||||||||
  < 17 | 468 | 77.4 | 0.84 | 0.66, 1.05 | 0.77 | 0.59, 0.99 | 379 | 73.1 | 0.92 | 0.71, 1.21 | 1.00 | 0.74, 1.34 | 408 | 79.4 | 1.28 | 0.98, 1.68 | 1.17 | 0.87, 1.58 |
 17–18 | 833 | 81.0 | 1.04 | 0.85, 1.27 | 0.93 | 0.75, 1.16 | 861 | 80.3 | 1.38 | 1.11, 1.73 | 1.38 | 1.08, 1.76 | 1010 | 81.5 | 1.47 | 1.19, 1.80 | 1.24 | 0.99, 1.54 |
 19 +  | 1735 | 80.4 | 1 |  | 1 |  | 2247 | 74.7 | 1 |  | 1 |  | 2191 | 75.1 | 1 |  | 1 |  |
Lives with partner | ||||||||||||||||||
 No | 367 | 76.5 | 0.79 | 0.61, 1.01 | 0.73 | 0.55, 0.97 | 317 | 66.2 | 0.57 | 0.45, 0.73 | 0.61 | 0.46, 0.80 | 353 | 73.6 | 0.79 | 0.61, 1.04 | 0.87 | 0.64, 1.18 |
 Yes | 2718 | 80.5 | 1 |  | 1 |  | 3192 | 77.4 | 1 |  | 1 |  | 3284 | 77.9 | 1 |  | 1 |  |
Parity | ||||||||||||||||||
 Primiparous | 1524 | 81.3 | 1.17 | 0.98, 1.39 | 1.03 | 0.86, 1.24 | 1877 | 79.1 | 1.45 | 1.22, 1.72 | 1.32 | 1.09, 1.59 | 1872 | 78.7 | 1.17 | 0.98, 1.39 | 1.08 | 0.90, 1.29 |
 Multiparous | 1480 | 78.8 | 1 |  | 1 |  | 1570 | 72.3 | 1 |  | 1 |  | 1684 | 76.0 | 1 |  | 1 |  |