Maternal and infant hospitalization costs associated with maternal pre-pregnancy body mass index in California, 2007–2011

Background: In the United States, the number of pregnant women who are overweight or obese is increasing. While such individuals are at increased risk of pregnancy complications, data regarding costs associated with pre-pregnancy body mass index (BMI) and maternal and infant outcomes are lacking. Objective: To estimate maternal and infant costs associated with pre-pregnancy BMI in a large cohort of pregnant women. Materials and methods: We conducted a retrospective cohort study of women with singleton, non-anomalous births in California from 2007 to 2011. Women with preexisting diabetes mellitus and chronic hypertension were excluded. Hospitalization costs were estimated separately for women and infants using hospital charges adjusted using a cost-to-charge ratio. These costs included hospitalization costs for admission for delivery only. We estimated the differences in median costs between seven categories of pre-pregnancy BMIs, including underweight (BMI <18.5), normal weight (BMI 18.5–24.9), overweight (BMI 25.0–29.9), class I obesity (BMI 30.0–34.9), class II obesity (BMI 35.0–39.9), class III obesity (BMI 40.0–49.9) and obesity with BMI ≥50.0. We also performed stratified analyses by mode of delivery and gestational age at delivery. We examined the length of stay for women and infants and estimated the gestational age at delivery. Analyses were conducted utilizing Kruskal-Wallis equality-of-populations rank tests with a significance cutoff of 0.05. Results: In a California cohort of 1,722,840 women, 787,790 (45.7%) had a pre-pregnancy BMI that was considered overweight or obese. The median maternal and infant costs of each pre-pregnancy BMI strata were significantly different when compared to other strata, with underweight and normal weight women having the lowest median costs ($11,581 and $11,721, respectively) and the most obese category (BMI ≥50) having the highest costs ($15,808). When stratified by mode of delivery and gestational age at delivery, this remained true. Hospitalization costs for women and infants with severe maternal morbidity were also significantly different based on maternal BMI. Comment: The hospitalization costs associated with each strata of BMI were significantly different when compared to each other and when stratified by mode of delivery and prematurity. This analysis allows for a greater understanding of the health care costs associated with different maternal pre-pregnancy BMI classes.