Maternal age potentiates the impact of operative birth on serious neonatal outcomes.

Pregnancies at the extremes of maternal age (<20 and >35) are associated with adverse obstetric and perinatal outcomes. There is limited evidence regarding the influence of maternal age on serious neonatal outcomes by mode of delivery. The aim of this study thus was to assess the relationship between maternal age and mode of delivery and its impact on a composite of serious neonatal outcomes. This was a retrospective cohort study of low risk women birthing at term in Australia's largest maternity hospital over a 7-year period. Intrapartum and perinatal outcomes were collated and a composite of severe adverse neonatal outcomes (SANO) was generated. Multiple regression was applied to adjust for confounders and generate adjusted odds ratios for the risk of SANO according to mode of delivery and maternal age. A total of 84,698 women were included in this study of which 1572 (1.9%) were aged <20 years, 7471 (8.8%) were aged 20-24 years, 20,125 (23.8%) were aged 25-29 years, 31,594 (37.3%) were aged 30-34 years, 19,371 (22.9%) were aged 35-40 years, 4280 (5.1%) were aged 40-44 years and 285 (0.3%) were aged ≥45 years. The incidence of SANO was significantly greater among adolescents compared to all other age groups. Overall, SANO was most likely to occur following Emergency Caesarean Section (EmCS) for severe intrapartum hemorrhage/uterine rupture compared to all other indications. Instrumental delivery was associated with the greatest odds of SANO (adjusted odds ratios (aOR) 3.31, 95% CI 3.08-3.55,  < .001) while spontaneous vaginal delivery (SVD) was associated with the lowest odds (aOR 0.46, 95% CI 0.43-0.48,  < .001). The adjusted odds for SANO was lowest in women aged 30-34 years (aOR 0.92, 95% CI 0.87-0.97,  < .001). The odds of SANO following an SVD increased with maternal age, with women aged 40-44 years having the highest odds. Similarly, the odds of SANO following an instrumental delivery increased with maternal age (age <20 years: aOR 2.21, 95% CI 1.38-3.54,  < .001 versus age 35-39 years: aOR 3.76, 95% CI 3.16-4.48,  < .001). This large retrospective cohort study has demonstrated that maternal age not only affects the mode of delivery and the incidence of adverse neonatal outcomes but that the effect of mode of delivery upon the risk of SANO is not independent of maternal age.