Parental age and preterm birth: a population-based cohort of nearly 3 million California livebirths from 2007 to 2012.

Purpose To assess the relationships between parental ages and preterm birth subtypes. Methods A population-based cohort analysis of California livebirths 2007-2012. Associations between maternal and paternal age with spontaneous and medically indicated preterm birth were estimated from Cox proportional hazard models. Parental age was modeled with restricted cubic splines to account for nonlinear relationships. Results Young paternal age was associated with increased hazard ratios for spontaneous and medically indicated preterm birth. Older fathers showed elevated hazards for preterm birth in crude analysis but after adjustment the relationship was generally not observed. Aging mothers showed increased hazard ratios for both preterm birth phenotypes. Conclusions After adjusting for parental demographics, births to younger fathers and older mothers had the highest risks for spontaneous preterm birth. The paternal influence on preterm birth was observed to be independent of maternal factors.