Linear association between maternal age and need of medical interventions at delivery in primiparae: a cohort of 21,235 singleton births

Objectives: We sought to investigate the potential association between maternal age and the need for active obstetrical intervention intrapartum in primiparas.Study design: Observational study over 14years (2001-2014) of all consecutive primiparous singleton births having delivered at the Centre Hospitalier Universitaire Hospitalier Sud Reunion's maternity (French overseas department, Indian Ocean).Results: Of the 21,235 singleton primiparous births, there were three significant linear associations between maternal age from 12years of age to 42+(all (2) for linear trend, p<.0001) (a) vaginal deliveries without any medical intervention, (b) rate of cesarean sections, and (c) rate of operative vaginal procedures. These three linear associations persisted when controlling for maternal obesity (30kg/m(2)), heavy babies (>3.5kg), and ethnicity. Using maternal age remained significantly an independent risk factor (p<.0001), after controlling for the major confounders: maternal BMI, maternal height, birthweight 3500g, p<.0001.Conclusions: Increasing maternal age has a linear association with vaginal deliveries without any medical intervention, rate of cesarean sections, and rate of operative vaginal procedures. These associations are independent of maternal BMI and maternal height. We currently do not have a specific explanation why younger women appear to be protected from requiring intrapartum obstetric intervention. Nevertheless, these strong facts deserve acknowledgement and further research.