Abstract: Breast cancer in pregnancy is a rare condition. The objective of our study was to describe the incidence, risk factors, and obstetrical outcomes of breast cancer in pregnancy. We conducted a population-based cohort study on 8.8 million births using data from the Healthcare Cost and Utilization Project – Nationwide Inpatient Sample from 1999–2008. The incidence of breast cancer was calculated and logistic regression analysis was used to evaluate the independent effects of demographic determinants on the diagnosis of breast cancer and to estimate the adjusted effect of breast cancer on obstetrical outcomes. There were 8,826,137 births in our cohort of which 573 cases of breast cancer were identified for an overall 10-year incidence of 6.5 cases per 100,000 births with the incidence slightly increasing over the 10-year period. Breast cancer appeared to be more common among women >35 years of age, odds ratio (OR) = 3.36 (2.84–3.97); women with private insurance plans, OR = 1.39 (1.10–1.76); and women who delivered in an urban teaching hospital, OR = 2.10 (1.44–3.06). After adjusting for baseline characteristics, women with pregnancy-associated breast cancer were more likely to have an induction of labor, OR = 2.25 (1.88, 2.70), but similar rates of gestational diabetes, preeclampsia, instrumental deliveries, and placental abruption. The incidence of breast cancer in pregnancy appears higher than previously reported with women over 35 being at greatest risk. Aside from an increased risk for induction of labor, women with breast cancer in pregnancy have similar obstetrical outcomes.