Relative risk for non-OU compared to OU by age groups in nulliparous women
| Age (years) | Unadjusted RR* (95% CI) | Adjusted RR*,† (95% CI) | Adjusted RR*,‡ (95% CI) |
|---|---|---|---|
| Maternal composite | |||
| 16–19 | 0.44 (0.38 to 0.53) | 0.45 (0.38 to 0.54) | 0.49 (0.42 to 0.58) |
| 20–24 | 0.51 (0.45 to 0.57) | 0.51 (0.45 to 0.58) | 0.55 (0.49 to 0.62) |
| 25–29 | 0.58 (0.53 to 0.64) | 0.59 (0.54 to 0.65) | 0.63 (0.57 to 0.70) |
| 30–34 | 0.60 (0.55 to 0.66) | 0.61 (0.56 to 0.67) | 0.66 (0.60 to 0.73) |
| 35–39 | 0.61 (0.54 to 0.68) | 0.62 (0.56 to 0.69) | 0.68 (0.61 to 0.76) |
| 40+ | 0.62 (0.49 to 0.80) | 0.66 (0.51 to 0.87) | 0.70 (0.53 to 0.93) |
| Augmentation | |||
| 16–19 | 0.33 (0.26 to 0.42) | 0.34 (0.27 to 0.44) | 0.37 (0.29 to 0.47) |
| 20–24 | 0.42 (0.35 to 0.51) | 0.43 (0.35 to 0.52) | 0.47 (0.39 to 0.57) |
| 25–29 | 0.49 (0.43 to 0.55) | 0.50 (0.45 to 0.57) | 0.56 (0.49 to 0.63) |
| 30–34 | 0.53 (0.47 to 0.60) | 0.55 (0.48 to 0.63) | 0.61 (0.53 to 0.71) |
| 35–39 | 0.54 (0.44 to 0.65) | 0.54 (0.46 to 0.64) | 0.61 (0.51 to 0.74) |
| 40+ | 0.50 (0.32 to 0.78) | 0.53 (0.33 to 0.84) | 0.58 (0.36 to 0.94) |
*Probability weights are incorporated to account for differences in the probability of a woman being selected for inclusion in the study arising from differences in each unit/trust's period of participation and the stratum-specific probabilities of selection of OUs.
†Adjusted for ethnic group, understanding of English, marital/partner status, BMI in pregnancy, index of multiple deprivation score quintile and gestation at delivery.
‡Adjusted for ethnic group, understanding of English, marital/partner status, BMI in pregnancy, index of multiple deprivation score quintile, gestation at delivery and complicating conditions identified at the start of care in labour.
BMI, body mass index; OU, obstetric unit.