BackgroundResearch on obesity in women of reproductive age is heterogeneous in gestational age and body mass index (BMI) classification and focused mostly on pregnancy-related rather than medical comorbidities. We studied the prevalences of pre-pregnancy BMI, chronic maternal and obstetric comorbidities, and delivery outcomes.MethodsRetrospective analysis of real-time data collected during deliveries in a single tertiary medical center. Pre-pregnancy BMI was classified into seven groups (kg/m2): underweight (BMI< 18.5), normal weight 1 (18.5 ≤ BMI < 22.5), normal weight 2 (22.5 ≤ BMI < 25.0), overweight 1 (25.0 ≤ BMI < 27.5), overweight 2 (27.5 ≤ BMI < 30.0), obese (30.0 ≤ BMI < 35.0), and morbidly obese (BMI≥ 35.0). Data were collected on maternal demographics, chronic medical and obstetric comorbidities, and delivery outcomes.ResultsIncluded were 13,726 women aged 18–50 years, with a gestational age of 240/7–416/7weeks. Pre-pregnancy weights were 61.4% normal, 19.8% overweight, 7.6% obese, and 3.3% morbidly obese. Smoking was more prevalent among morbidly obese than among normal weight women. Obese and morbidly obese women were older and had more diabetes mellitus, hypertension, preeclampsia/eclampsia, and prior cesarean deliveries than normal weight parturients. Obese and morbidly obese women were also less likely to have a non-spontaneous conception, enter labor spontaneously (observed in the full study population and in a subgroup of term parturients), and were more likely to undergo cesarean rather than vaginal delivery. Subgroup analysis of primiparous women yielded similar results.ConclusionsWe identified a potential association between pre-pregnancy obesity and morbid obesity and higher rates of obstetric comorbidities, less natural conception and spontaneous labor, and more cesarean deliveries and adverse delivery outcomes. It remains to be seen if these findings remain after adjustment and whether they are related to obesity, treatment, or both.Supplementary InformationThe online version contains supplementary material available at 10.1186/s44158-023-00105-7.