Purpose: To characterize and understand the demographics (age and body mass index, BMI) of a cohort of women who delivered at a single institution over an 11-year period. The purpose of this analysis is to look for effects over time of demographic characteristics on mode of delivery.Methods: Retrospective analysis of singleton deliveries between 2004-2014, n = 27,729; level 1 perinatal center, university hospital setting. Data were extracted from the digital birth registry. All statistical analyses were done using R version 3.5.1. Variables analyzed were: age, BMI, and mode of delivery (in the current and any prior pregnancies).Results: Mean age increased from 31.1 ± 5.2 years in 2004 to 31.5 ± 5.0 years in 2014 (p < 0.001, eta2 = 0.0006). Mean BMI before pregnancy increased from 23.7 ± 4.5 to 24.7 ± 5.2 kg/m2. Mean BMI at delivery increased from 28.5 ± 4.7 to 29.6 ± 5.2 kg/m2 (p < 0.001, eta2 = 0.0049). Regarding maternal age, patients with elective Cesarean section (CS) (32.5 ± 5.3 years), emergency CS (31.6 ± 5.6 years) and CS in labor (31.4 ± 5.3 years) were older compared to those with spontaneous (31.0 ± 5.2 years) or instrument-assisted vaginal delivery such as vacuum (31.0 ± 5.0 years) and forceps (30.2 ± 5.4 years). Among the multiparous patients, the mode of delivery in prior pregnancies is the variable with the greatest effect on the mode of delivery in any subsequent pregnancies. The mode of delivery was: spontaneous (55.5%), vaginal operative including vacuum and forceps (8.8%), and Cesarean section (35.7%).Conclusions: Increase of age and BMI over years is significant, but very small and in a range which seems not clinically relevant. Previous births have the strongest effects on mode of delivery in the current pregnancy. [ABSTRACT FROM AUTHOR]