The effect of maternal age and planned place of birth on intrapartum outcomes in healthy women with straightforward pregnancies: secondary analysis of the Birthplace national prospective cohort study

OBJECTIVES: To describe the relationship between maternal age and intrapartum outcomes in 'low-risk' women; and to evaluate whether the relationship between maternal age and intrapartum interventions and adverse outcomes differs by planned place of birth.

DESIGN: Prospective cohort study.

SETTING: Obstetric units (OUs), midwifery units and planned home births in England.

PARTICIPANTS: 63 371 women aged over 16 without known medical or obstetric risk factors, with singleton pregnancies, planning vaginal birth.

METHODS: Log Poisson regression was used to evaluate the association between maternal age, modelled as a continuous and categorical variable, and risk of intrapartum interventions and adverse maternal and perinatal outcomes.

MAIN OUTCOME MEASURES: Intrapartum caesarean section, instrumental delivery, syntocinon augmentation and a composite measure of maternal interventions/adverse outcomes requiring obstetric care encompassing augmentation, instrumental delivery, intrapartum caesarean section, general anaesthesia, blood transfusion, third-degree/fourth-degree tear, maternal admission; adverse perinatal outcome (encompassing neonatal unit admission or perinatal death).

RESULTS: Interventions and adverse maternal outcomes requiring obstetric care generally increased with age, particularly in nulliparous women. For nulliparous women aged 16-40, the risk of experiencing an intervention or adverse outcome requiring obstetric care increased more steeply with age in planned non-OU births than in planned OU births (adjusted RR 1.21 per 5-year increase in age, 95% CI 1.18 to 1.25 vs adjusted RR 1.12, 95% CI 1.10 to 1.15) but absolute risks were lower in planned non-OU births at all ages. The risk of neonatal unit admission or perinatal death was significantly raised in nulliparous women aged 40+ relative to women aged 25-29 (adjusted RR 2.29, 95% CI 1.28 to 4.09).

CONCLUSIONS: At all ages, 'low-risk' women who plan birth in a non-OU setting tend to experience lower intervention rates than comparable women who plan birth in an OU. Younger nulliparous women appear to benefit more from this reduction than older nulliparous women.