| 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) | 4035 | 88.2 | Â | Â | Â | Â | 3652 | 78.3 | (76.8, 79.8) | Â | Â | Â | 3438 | 73.7 | (72.2, 75.2) | Â | Â | Â |
Age of Mother | ||||||||||||||||||
 16–19 | 79 | 79.1 | 0.42 | 0.24, 0.73 | 0.35 | 0.19, 0.65 | 46 | 80.0 | 0.92 | 0.46, 1.82 | 0.98 | 0.44, 2.14 | 37 | 87.4 | 2.16 | 0.92, 5.08 | 2.14 | 0.89, 5.15 |
 20–24 | 457 | 86.1 | 0.68 | 0.49, 0.95 | 0.73 | 0.50, 1.06 | 251 | 69.8 | 0.53 | 0.40, 0.71 | 0.60 | 0.43, 0.83 | 245 | 69.5 | 0.71 | 0.54, 0.94 | 0.77 | 0.57, 1.04 |
 25–29 | 1082 | 88.3 | 0.84 | 0.64, 1.10 | 0.82 | 0.61, 1.09 | 837 | 76.0 | 0.73 | 0.58, 0.92 | 0.78 | 0.61, 0.99 | 790 | 68.7 | 0.69 | 0.57, 0.83 | 0.71 | 0.58, 0.87 |
 30–34 | 1426 | 90.0 | 1 |  | 1 |  | 1426 | 81.3 | 1 |  | 1 |  | 1347 | 76.2 | 1 |  | 1 |  |
 35–39 | 780 | 89.4 | 0.94 | 0.69, 1.27 | 0.90 | 0.66, 1.24 | 862 | 81.0 | 0.98 | 0.78, 1.23 | 1.01 | 0.79, 1.29 | 839 | 75.2 | 0.95 | 0.78, 1.16 | 0.94 | 0.77, 1.16 |
 40 +  | 212 | 87.4 | 0.77 | 0.48, 1.22 | 0.72 | 0.45, 1.15 | 230 | 84.4 | 1.24 | 0.83, 1.86 | 1.34 | 0.87, 2.07 | 180 | 80.9 | 1.33 | 0.89, 1.98 | 1.35 | 0.88, 2.07 |
Ethnicity | ||||||||||||||||||
 White | 3394 | 91.2 | 1 |  | 1 |  | 3121 | 81.2 | 1 |  | 1 |  | 2945 | 74.8 | 1 |  | 1 |  |
 Mixed | 74 | 83.9 | 0.50 | 0.26, 0.97 | 0.50 | 0.26, 0.98 | 80 | 70.8 | 0.56 | 0.32, 0.99 | 0.56 | 0.33, 0.96 | 73 | 65.9 | 0.65 | 0.40, 1.06 | 0.63 | 0.38, 1.03 |
 Asian | 348 | 75.3 | 0.29 | 0.22, 0.39 | 0.28 | 0.21, 0.38 | 226 | 69.2 | 0.52 | 0.38, 0.71 | 0.55 | 0.39, 0.76 | 256 | 66.6 | 0.67 | 0.52, 0.87 | 0.67 | 0.51, 0.87 |
 Black | 124 | 80.7 | 0.40 | 0.26, 0.62 | 0.43 | 0.26, 0.71 | 72 | 67.4 | 0.48 | 0.29, 0.81 | 0.55 | 0.32, 0.95 | 99 | 75.7 | 1.05 | 0.63, 1.75 | 0.98 | 0.59, 1.64 |
 Other | 16 | 69.6 | 0.22 | 0.09, 0.55 | 0.20 | 0.08, 0.50 | 53 | 74.0 | 0.66 | 0.33, 1.32 | 0.52 | 0.26, 1.04 | 17 | 64.1 | 0.60 | 0.25, 1.47 | 0.63 | 0.26, 1.54 |
IMD | ||||||||||||||||||
 1 (least advantaged) | 726 | 82.3 | 0.39 | 0.29, 0.54 | 0.69 | 0.48, 0.98 | 524 | 71.4 | 0.47 | 0.36, 0.62 | 0.65 | 0.49, 0.88 | 493 | 71.0 | 0.81 | 0.63, 1.02 | 0.92 | 0.72, 1.18 |
 2 | 858 | 88.0 | 0.62 | 0.44, 0.86 | 0.99 | 0.69, 1.41 | 694 | 77.5 | 0.65 | 0.50, 0.85 | 0.88 | 0.66, 1.17 | 653 | 74.0 | 0.94 | 0.75, 1.18 | 1.05 | 0.83, 1.33 |
 3 | 843 | 91.2 | 0.88 | 0.62, 1.25 | 1.07 | 0.74, 1.54 | 773 | 82.0 | 0.87 | 0.67, 1.13 | 1.00 | 0.76, 1.31 | 719 | 74.1 | 0.94 | 0.75, 1.17 | 0.99 | 0.79, 1.25 |
 4 | 785 | 91.4 | 0.90 | 0.63, 1.29 | 1.01 | 0.69, 1.47 | 829 | 81.3 | 0.83 | 0.64, 1.07 | 0.87 | 0.66, 1.13 | 816 | 75.6 | 1.02 | 0.82, 1.27 | 1.01 | 0.81, 1.26 |
 5 (most advantaged) | 823 | 92.2 | 1 |  | 1 |  | 832 | 84.1 | 1 |  | 1 |  | 757 | 75.2 | 1 |  | 1 |  |
Education | ||||||||||||||||||
  < 17 | 661 | 86.4 | 0.69 | 0.52, 0.91 | 0.66 | 0.49, 0.90 | 375 | 74.4 | 0.70 | 0.53, 0.91 | 0.80 | 0.59, 1.09 | 353 | 69.4 | 0.72 | 0.57, 0.92 | 0.73 | 0.57, 0.94 |
 17–18 | 1056 | 86.4 | 0.68 | 0.54, 0.87 | 0.62 | 0.47, 0.81 | 820 | 76.3 | 0.77 | 0.63, 0.96 | 0.84 | 0.66, 1.06 | 889 | 71.4 | 0.80 | 0.67, 0.95 | 0.82 | 0.68, 0.99 |
 19 +  | 2282 | 90.3 | 1 |  | 1 |  | 2426 | 80.6 | 1 |  | 1 |  | 2165 | 75.8 | 1 |  | 1 |  |
Lives with partner | ||||||||||||||||||
 No | 456 | 83.7 | 0.62 | 0.47, 0.81 | 0.77 | 0.56, 1.05 | 324 | 69.9 | 0.57 | 0.45, 0.74 | 0.80 | 0.59, 1.07 | 330 | 72.2 | 0.91 | 0.71, 1.16 | 0.95 | 0.73, 1.24 |
 Yes | 3582 | 83.7 | 1 |  | 1 |  | 3328 | 80.2 | 1 |  | 1 |  | 3108 | 74.0 | 1 |  | 1 |  |
Parity | ||||||||||||||||||
 Primiparous | 1999 | 89.5 | 1.27 | 1.03, 1.58 | 1.24 | 0.98, 1.56 | 1926 | 81.1 | 1.34 | 1.12, 1.60 | 1.27 | 1.04, 1.54 | 1754 | 74.2 | 1.05 | 0.90, 1.23 | 1.04 | 0.86, 1.23 |
 Multiparous | 1952 | 87.0 | 1 |  | 1 |  | 1663 | 76.2 | 1 |  | 1 |  | 1604 | 73.2 | 1 |  | 1 |  |