Association between maternal age (per 5-year increase) and maternal and perinatal outcomes in low-risk women aged between 16 and 40 years old (inclusive)
| Nulliparous women | Multiparous women | |||||||
|---|---|---|---|---|---|---|---|---|
| Unadjusted* | Adjusted*,† | Unadjusted* | Adjusted*,† | |||||
| RR | (95% CI) | RR | (95% CI) | RR | (95% CI) | RR | (95% CI) | |
| Maternal composite | 1.13 | (1.11 to 1.16) | 1.13 | (1.11 to 1.16) | 1.07 | (1.03 to 1.13) | 1.08 | (1.03 to 1.14) |
| OU‡ | 1.13 | (1.11 to 1.16) | 1.12 | (1.10 to 1.15) | ||||
| Non-OU‡ | 1.22 | (1.19 to 1.26) | 1.21 | (1.18 to 1.25) | ||||
| Wald test for interaction | p<0.001*,§ | Wald test for interaction | p=0.34*,§ | |||||
| Augmentation | 1.13 | (1.09 to 1.16) | 1.12 | (1.08 to 1.17) | 1.00 | (0.92 to 1.08) | 1.01 | (0.92 to 1.11) |
| OU‡ | 1.13 | (1.09 to 1.17) | 1.12 | (1.07 to 1.17) | ||||
| Non-OU‡ | 1.25 | (1.20 to 1.31) | 1.23 | (1.18 to 1.28) | ||||
| Wald test for interaction | p<0.001*,§ | Wald test for interaction | p=0.24*,§ | |||||
| Instrumental delivery | 1.20 | (1.13 to 1.26) | 1.18 | (1.12 to 1.25) | 1.14 | (1.04 to 1.25) | 1.15 | (1.05 to 1.27) |
| Wald test for interaction | p=0.18*,§ | Wald test for interaction | p=0.06*,§ | |||||
| Intrapartum caesarean section | 1.27 | (1.23 to 1.31) | 1.27 | (1.23 to 1.32) | 1.16 | (1.07 to 1.26) | 1.16 | (1.06 to 1.28) |
| Wald test for interaction | p=0.26*,§ | Wald test for interaction | p=0.50*,§ | |||||
| General anaesthesia | 1.06 | (0.93 to 1.20) | 1.06 | (0.92 to 1.22) | 1.05 | (0.87 to 1.27) | 1.09 | (0.91 to 1.32) |
| Wald test for interaction | p=0.83*,§ | Wald test for interaction | p=0.15*,§ | |||||
| Maternal blood transfusion | 1.09 | (0.97 to 1.23) | 1.13 | (0.95 to 1.34) | 1.23 | (0.95 to 1.60) | 1.24 | (0.94 to 1.62) |
| Wald test for interaction | p=0.38*,§ | Wald test for interaction | p=0.44*,§ | |||||
| Third/fourth degree perineal tear | 1.17 | (1.09 to 1.27) | 1.12 | (1.02 to 1.23) | 1.10 | (0.98 to 1.23) | 1.01 | (0.89 to 1.15) |
| Wald test for interaction | p=0.43*,§ | Wald test for interaction | p=0.29*,§ | |||||
| Maternal admission for higher level care | 1.28 | (1.03 to 1.58) | 1.46 | (1.07 to 1.99) | 1.40 | (1.01 to 1.92) | 1.49 | (1.06 to 2.10) |
| Wald test for interaction | p=0.41*,§ | Wald test for interaction | p=0.15*,§ | |||||
| Perinatal composite | 1.07 | (0.97 to 1.17) | 1.06 | (0.95 to 1.17) | 1.02 | (0.87 to 1.19) | 0.98 | (0.84 to 1.15) |
| Wald test for interaction | p=0.92*,§ | Wald test for interaction | p=0.66*,§ | |||||
*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, gestation at delivery and planned place of birth (OU vs AMU vs FMU vs home).
‡Results in these rows were adjusted for ethnic group, understanding of English, marital/partner status, BMI in pregnancy, index of multiple deprivation score quintile and gestation at delivery.
§p for interaction; results in these rows were adjusted for ethnic group, understanding of English, marital/partner status, BMI in pregnancy, index of multiple deprivation score quintile, gestation at delivery and planned place of birth (OU vs non-OU).
AMU, alongside midwifery unit; BMI, body mass index; FMU, freestanding midwifery unit; OU, obstetric unit.